    
|
 Helping San Diego, California and beyond since 1997 |
|
|
Helping San Diego, California and beyond since 1997 |
Click here and add this page to your favorites!
|
Encyclopedia Britannica - Main :: RAY-RHU |
|
|
REPRODUCTIVE SYSTEM, IN ANATOMY .The reproductive system in some parts of its course shares structures in common with the urinary system (q.v.). In this article the following structures will be dealt with. In the male the testes, epididymis, vasa deferentia, vesiculae seminales, prostate, penis and urethra. In the female the ovaries, Fallopian tubes, uterus, vagina and vulva. Male Reproductive Organs. The testes or testicles are the glands in which the male reproductive cells are formed. They lie, one on each side, in the scrotum surrounded by the tunica vaginalis (see COELOM and SEROUS MEMBRANES).' Each is an oval gland about one and a half inches long with its long axis directed downward, backward and inward. There is a strong fibrous coat called the tunica albuginea, from which vertical and horizontal
seminiferous tubes in the two glands is little short of a mile. (See fig. I.) At the posterior part of the testis the fibrous sheath is greatly thickened to form the mediastinum testis, and contains a plexus of tubules called the rete testis (see fig. 1), into which the seminiferous tubes open. In this way the secretion of the gland is carried to its upper and gm back part, whence from fifteen From A. F. Dixon, Cunningham's Text-book to twenty small tubes (vasa of Anatomy. efferentia) pass to the epidi- FIG. I.Diagram to illustrate the dymis. Each of these is dymisure of the testis and epidiconvoluted before opening, cv. Conivasculosi. s.f. Seminiferous and forms what is known as c. Globus major. tubule. g.m'. Globus Minor. v.d. Vas deferens. a onus vasculosus. r.v. Rete testis ve. Vas efferens. Under the microscope the s. Septula testis. vr. Tubuli recti. seminiferous tubules are seen to consist of a basement membrane surrounding several layers of epithelial cells, some of which are constantly being transformed into spermatozoa or male sexual cells. The epididymis (see fig. I) is a soft body lying behind the testis; it is enlarged above to form the globus major or head, while below is a lesser swelling, the globus minor or tail. The whole epididymis is made up of a convoluted tube about 20 ft. long, from which one long diverticulum (vas aberrans) comes off. Between the globus major and the testis two small vesicles called the hydatids of Morgagni are often found. The vas deferens is the continuation of the tube of the epididymis and starts at the globus minor; at first it is convoluted, but soon becomes straight, and runs up on the inner (mesial) side of the epididymis to the external abdominal ring in the abdominal wall
wall
: inward to meet its fellow at the back of the bladder, just above the prostate. The whole length of the vas is 12 to 18 in. and it is remarkable for the great thickness of its muscular walls, which gives it the feeling of a piece of whipcord when rolled between the finger and thumb. A little above the globus major a few scattered tubules are found in children in front of the cord; these form the rudimentary structure known as the organ of Giraldes or paradidymis. As the vas deferens approaches the prostate it enlarges and becomes slightly sacculated to act as a reservoir for the secretion of the testis; this part is the ampulla (see fig. 2). Ureter Great sciatic notch Vas deferens Spine of ischium Vas deferens Levator ani Prostate Ischio-rectal fossa Tuberosity of j ischium s The vesiculae seminales are sac-like diverticula, one on each side, from the lower part of the ampullae of the vasa deferentia. They are about 2 in. long and run outward behind the bladder and parallel to the upper margin of the prostate for some little distance, but usually turn upward near their blind extremity. When carefully dissected and unravelled each is found to consist of a thick tube, about 5 in. long, which is sharply bent upon itself two or three times, and also has several short, sac-like pouches or diverticula. The vesiculae seminales are muscular sacs with a mucous lining which is thrown into a series of delicate net-like folds. The convolutions are held together by the pelvic cellular tissue, and by involuntary muscle continuous with that of the bladder. It is probable that these vesicles are not reservoirs, as was at one time thought, but form some special secretion which mixes with that of the testes. Where the vesiculae join the ampullae of the vasa deferentia the ejaculatory ducts are formed; these are narrow and thin-walled,and run, side by side, through the prostate to open into the floor of the prostatic urethra. The prostate is partly a muscular and partly a glandular structure, situated just below the bladder and traversed by the urethra; it is of a somewhat conical form with the base upward in contact with the bladder. Both vertically and transversely it measures about an inch and a quarter, while antero-posteriorly it is only about three-quarters of an inch, though its size is liable to great variation. It is enclosed in a fibrous capsule from which It is separated by the prostatic plexus of veins anteriorly. It is often described as formed of three lobes two lateral and a median or posterior, but careful sections and recent
Microscopically the prostate consists of masses of long, slender, slightly branching glands, embedded in unstriped muscle and fibrous tissue; these glands open by delicate ducts (about twenty in number) into the prostatic urethra, which will be described later. In the anterior part of the gland are seen bundles of striped muscle fibres, which are of interest
Seminal vesicle tomy of the gland _ Ampulla of vas deferens 1 Cut end of great sacro- IS studied: they are sciatic ligament better seen in Common ejaculatory duct young than in old prostates. The male urethra begins at the bladder and runs through the prostate and perineum to the penis, which it traverses as far as the tip. It is divided into a prostatic, membranous and spongy part, From A. F. Dixon, Cunningham's Text-book of Anatomy. and is altogether about Vasa Deferentia from behind. The prostatic urethra The coccyx and the sacro-sciatic ligaments, together with the muscles attached to them, have been removed. runs downward The levatores ani have been separated along the median raphe, and drawn
terior than the pos- terior part. It is about an inch and a quarter long, and in the middle of the gland it bends forward forming an angle (see fig. 5); here it is from a third to half an inch wide, though at the base and apex of the prostate it is narrower. When it is slit open from in front a longitudinal ridge
Cut end of rectum Apex of sacrum Great sciatic notch Ureter Peritoneum Spine of ischium Bladder wall Levator ani Tuberosity of ischium Posterior superior iliac spine Ischio-rectal fossa Cut end of rectum External sphincter ani Gluteus maximus the prostate the urethra runs more forward for about three-quarters of an inch, lying between the two layers of the triangular From C. S. Wallace's Prostatic Enlargement). of the bladder above, prostate and bulb below. ligament, both of which it pierces. This is known as the membranous urethra, and is very narrow, being gripped by the compressor urethrae muscle. The spongy urethra is that part which is enclosed in the penis after piercing the anterior layer of the triangular ligament. At first it lies in the substance of the bulb and, later, of the corpus spongiosum, while finally it passes through the glans. In the greater part of its course it is a transverse slit, but ih traversing the glans it enlarges considerably to form the fossa navicularis, and here, in transverse section, it looks like an inverted T (I), then an inverted Y (A), and finally at its opening From C. S. Wallace's Prostatic Enlargement. (external meatus) a vertical slit. Into the whole length of the urethra mucous glands (glands of Littre) open, and in the roof of ' Figs. 3, 4, 5 and 9 of this article are redrawn from Cuthbert S. Wallace's Prostatic Enlargement by permission of the managers of The Oxford Medical Publications.the fossa navicularis the mouth of one of these is sometimes so large that it may engage the point of a small catheter and is known as the lacuna magna. As a rule the meatus is the narrowest part of the whole canal. Opening into the spongy urethra where it passes through the bulb are the ducts of two small glands known as Cowper's glands, which lie on each side of the membranous urethra and are best seen in childhood. The penis is the intromittent organ of generation, and is made up of three cylinders of erectile tissue, covered by skin and subcutaneous tissue without fat. In a transverse section two of these cylinders (the corpora cavernosa) are placed above, side by side, while one, the corpus spongiosum, is below. Posteriorly, at what is known as the root of the penis, the two corpora cavernosa diverge, become more and more fibrous in structure, and are attached on each side to the rami of the ischium, while the corpus spongiosum becomes more vascular and enlarges to form the bulb. It has already been pointed out that the whole length of the corpus spongiosum is traversed by the urethra. The anterior part of the penis is formed by the glans, a bell-shaped structure, apparently continuous with the corpus spongiosum, and having the conical ends of the corpora cavernosa fitted into depressions on its posterior surface. On the dorsum of the penis the rim of the bell-shaped glans projects beyond the level of the corpora cavernosa, and is From C. S. Wallace's Froslatic Enlargement. showing one of the ejaculatory ducts. known as the corona glandis. The skin of the penis forms a fold which covers the glans and is known as the prepuce or foreskin; when this is drawn
Female Reproductive Organs. The ovary is an organ which in shape and size somewhat resembles a large almond, though its appearance varies considerably in different individuals, and at different times of life. It lies in the side wall of the pelvis with its long axis nearly vertical and having its blunt end (tubal pole) upward. Its more pointed lower end is attached to the uterus by the liga ment of the ovary, while its anterior border has a short reflection of peritoneum, known as the mesovarium, running forward to the broad ligament of the uterus. It is through this anterior border that the vessels and nerves enter and leave the gland. Under the microscope the ovary is seen to be covered by a layer of cubical cells, which are continuous near the anterior border with the cells of the peritoneum. Deep to these is the ovarian stroma, composed of fibrous tissue, and embedded in it are numerous nests of epithelial cells, the Graafian follicles, in various stages of development. During the child-bearing period of life some of these will be nearing the ripe condition, and if one such be looked at it will be seen to contain one large cell, the ovum, surrounded by a mass of small cells forming the discus proligerus. At one point this is continuous with a layer of cells called the stratum granulosum which lines the outer wall of the follicle, but elsewhere the two layers are separated by fluid, the liquor folliculi. When the follicle bursts, as it does in time, the ovum escapes on to the surface of the ovary. The Fallopian tubes receive the ova and carry them to the uterus. That end of each which lies in front of the ovary is called the fimbriated extremity, and has a number of fringes (fimbriae) hanging from it; one of the largest of these is the ovarian fimbria and is attached to the upper or tubal pole of the ovary. The small opening among the fimbriae by which the tube communicates with the peritoneal cavity is known as the ostium abdominale, and from this the lumen of the tube runs from four to four and a half inches, until it opens into the cavity of the uterus by an extremely small opening. In the accompanying figure (fig. 6) the Fallopian tube and ovary Parovarium Ligament Fallopian tube I Ovary of ovary Uterus are pulled out from the uterus; this, as has been explained, is not the position of the ovary in the living body, nor is it of the tube, the outer half of which lies folded on the front and inner surface of the ovary, The Fallopian tubes, like many other tubes in the body, are made chiefly of unstriped muscle, the outer layer of which is longitudinal and the inner circular; deep to this are the submucous and mucous coats, the latter being lined with ciliated epithelium (see EPITHELIAL TrssuEs), and thrown into longitudinal pleats. Superficially the tube is covered by a serous coat of peritoneum. The calibre gradually contracts from the peritoneal to the uterine opening. The uterus or womb is a pear-shaped, very thick-walled, muscular bag, lying in the pelvis between the bladder and rectum. In the non-pregnant condition it is about three inches long and two in its broadest part, which is above. The upper half or body of the uterus is somewhat triangular with its base upward, and has an anterior surface which is moderately flat, and a posterior convex. The lower half is the neck or cervix and is cylindrical; it projects into the anterior wall of the vagina, into the cavity of which it opens by the os uteri externum. This opening in a uterus which has never been pregnant is a narrow transverse slit, rarely a circular aperture, but in those uteri in which pregnancy has occurred the slit is much wider and its lips are thickened and gaping and oftenscarred. The interior of the body of the uterus shows a comparatively small triangular. cavity (see fig. 6, $), the anterior and posterior walls of which are in contact. The base of the triangle is upward, and at each lateral angle one of the Fallopian tubes opens. The apex leads into the canal of the cervix, but between the two there is a slight constriction known as the os uteri internum. The canal of the cervix is about an inch long, and is spindle-shaped when looked at from in front; its anterior and posterior walls are in contact, and its lining mucous membrane is raised into a pattern which, from its likeness to a cypress twig, is called the arbor vitae. This arrange-. ment is obliterated after the first pregnancy. On making a mesial vertical section of the uterus the cavity is seen as a mere slit which is bent about its middle to form an angle the opening of which is forward. A normal uterus is therefore bent forward on itself, or anteflexed. In addition to this, its long axis forms a marked angle with that of the vagina, so that the whole uterus is bent forward or anteverted. As a rule, in adults the uterus is more or less on one side of the mesial plane of the body. From each side of the uterus the peritoneum is reflected outward, as a two-layered sheet, to the side wall of the pelvis; this is the broad ligament, and between its layers lie several structures of importance. Above, there is the Fallopian tube, already described; below and in front is the round ligament; behind, the ovary projects backward, and just above this, when the broad ligament is stretched out as in fig. 6, are the epoophoron and paroophoron with the duct of Gartner. The round ligament is a cord of unstriped muscle which runs from the lateral angle of its own side of the uterus forward to the internal abdominal ring, and so through the inguinal canal to the upper part of the labium majus. The epoophoron or parovarium is a collection of short tubes which radiate from the upper border of the ovary when the broad ligament is pulled out as in fig. 6. It is best seen in very young children and represents the vasa efferentia in. the male. Near the ovary the tubes are closed, but nearer the Fallopian tube they open into another tube which is nearly at right angles to them, and which runs toward the uterus, though in the human subject it is generally lost before reaching that organ. It is known as the duct of Gartner, and is the homologue of the male epididymis and vas deferens. Some of the outermost tubules of the epoophoron are sometimes distended to form hydatids. Nearer the uterus than the epoophoron a few scattered tubules are occasionally found which are looked upon as the homologue of the organ of Giraldes in the male, and are known as the paroophoron. The vagina is a dilatable muscular passage, lined with mucous membrane, which leads from the uterus to the external generative organs; its direction is, from the uterus, downward and forward, and its anterior and posterior walls are in contact, so that in a horizontal
The vulva or pudendum comprises all the female external generative organs, and consists of the mons Veneris, labia majora and minora, clitoris, urethral orifice, hymen, bulbs of the vestibule, and glands of Bartholin. The mons Veneris is the Lateral angle of uterus A A. F. Dixon, Cunningham's Text-Book of Anatomy. a, b and c, the isthmus tubae, the ligament of the ovary, and the round ligament of the right side cut short. B. Diagrammatic Representation of the Uterine Cavity opened up from in front. Vaginal cavity B elevation
The clitoris is the representative of the penis, and consists of two corpora cavernosa which posteriorly diverge to form the crura clitoridis, and are attached to the ischium; the organ is about an inch and a half long, and ends anteriorly in a rudimentary glans which is covered by the junction of the labia minora; this junction forms the prepuce of the clitoris. The orifice of the urethra is about an inch below the glans clitoridis and is slightly puckered. The hymen is a fold of mucous membrane which surrounds the orifice of the vagina and is usually only seen in the virgin. As has been pointed out above, it is represented in the male by the fold at the opening of the uterus masculinus. Occasionally the hymen is imperforate and then gives rise to trouble in menstruation. The bulbs of the vestibule are two masses of erectile tissue situated one on each side of the vaginal orifice: above they are continued up to the clitoris; they represent the bulb and the corpus spongiosum of the male, split into two, and the fact that they are so divided accounts for. the urethra failing to be enclosed in the clitoris as it is in the penis. The glands of Bartholin are two oval bodies about half an inch long, lying on each side of the vagina close to its opening; they represent Cowper's glands in the male, and their ducts open by minute orifices between the hymen and the labia minora. From the above description it will be seen that all the parts of the male external genital organs are represented in the female, though usually in a less developed condition, and that, owing to the orifice of the vagina, they retain their original bi-lateral form. For further details see Quain's Anatomy (London: Longmans
Longmans
Embryology. The development of the reproductive organs is so closely interwoven with that of the urinary that some reference from this article to that on the URINARY SYSTEM is necessary. It will here be convenient to take up the development at the stage depicted in the accompanying figure (fig. 7), in which the genital ridge
sixth
Recent
In the female the same growth of epithelial cords into the mesenchyme of the genital ridge takes place, but each one is From A. F. Dixon, Cunningham's Text-Book of Anatomy. a. shows position of germinal epithelium. distinguished by a bulging toward its middle, in which alone the large germ cells are found. Eventually this bulging part is broken up into a series of small portions, each of which contains one germ cell or ovum, and gives rise to a Graafian follicle. Mesonephric cords appear as in the male; they do not enter the ovary, however, but form a transitory network (rete ovarii) in the mesovarium. As each genital gland enlarges it remains attached to the rest of the intermediate cell mass by a constricted fold of the coelomic membrane, known as the mesorchium in the male, and the mesovarium in the female. Lying dorsal to the genital ridge in the intermediate cell mass is the mesonephros, consisting Pro. N. Pronephros. N. Nephrostome. M.N. Mesonephros. M.C. Malpighian corpuscle. Mt.N. Metanephros. T. Testis. B. Bladder. E. Epididymis. Clo. Cloaca. O.G. Organ of Giraldes. R. Rectum. V.D. Vas deferens. M.D. Mullerian duct. U.M. Uterus masculinus. W.D. Wolffian duct. O. Ovary. Ur. Ureter. Ep.O. Epobphoron. S.H. Sessile hydatid. Par.O. Parotiphoron. P.H. Pedunculated hydatid. F.T. Fallopian tube. S.G. Sexual gland. U. Uterus. of numerous tubules which open into the Wolffian duct. This at first is an important excretory organ, but during development becomes used for other purposes. In the male, as has been shown, it may form the rete testis, and certainly forms the vasa efferentia and globus major of the epididymis: in addition to these, some of its separate tubes probably account for the vas aberrans and the organ of Giraldes (see fig. 8, E. and O.G.). In the female the tubules of the epoophoron represent the main part, Clo. U.M. while the paroophoron, like the organ of Giraldes in the male, is probably formed from some separate tubes (see fig. 8, Ep. O. and Par. O.). The Wolffian duct, which, in the early embryo, carries the excretion of the mesonephros to the cloaca, forms eventually the body and tail of the epididymis, the vas deferens, and ejaculatory duct in the male, the vesicula seminalis being developed as a pouch in its course. In the female this duct is largely done away with, but remains as the collecting tube of the epoophoron, and in some mammals as the duct of Gartner, which runs down the side of the vagina to open into the vestibule. The Mullerian duct, as it approaches the cloaca, joins its fellow of the opposite side, so that there is only one opening into the ventral cloacal wall. In the male the lower part only of it remains as the uterus masculinus (fig. 8, U.M.), but in the female the Fallopian tubes, uterus, and probably the vagina, are all formed from it (fig. 8, F.T. and U.). In both sexes a small hydatid or vesicle is liable to be formed at the beginning of both the Wolffian and Mullerian duct (fig. 8, P.H. and S.H.); in the male these are close together in front of the globus major of the epididymis, and are known as the sessile and pedunculated hydatids of Morgagni. In the female there is a hydatid among the fimbriae of the Fallopian tube which of course is Mullerian and corresponds to the sessile hydatid in the male, while another is often found at the beginning of the collecting tube of the epoophoron and is probably formed by a blocked mesonephric tubule. This is the pedunculated hydatid of the male. The development of the vagina, as Berry Hart (Journ. Anat. and Phys. xxxv. 330) has pointed out, is peculiar. Instead of the two Mullerian ducts joining to form the lumen of its lower third, as they do in the case of the uterus and its upper two-thirds, they become obliterated, and their place is taken by two solid cords of cells, which Hart thinks are derived from the Wolffian ducts and are therefore probably of ectodermal origin, though this is open to doubt. These cords later become canalized and the septum between them is obliterated. The common chamber, or cloaca, into which the alimentary, urinary and reproductive tubes open in the foetus, has the urinary bladder (the remains of the allantois) opening from its ventral wall (see PLACENTA and URINARY SYSTEM). During development the alimentary or anal part of the cloaca is separated from the urogenital, and in the article ALIMENTARY SYSTEM the hitherto accepted method of this separation is described. The question has, however, lately been reinvestigated by F. Wood Jones, who says that the anal part is completely shut off from the urogenital and ends in a blind pouch which grows toward the surface and meets a new ectodermal depression, the main point being that the permanent anus is not, according to him, any part of the original cloacal aperture, but a new perforation. This description is certainly more in harmony with the malformations occurring in this region than the old one, and only awaits confirmatory evidence to be generally accepted. The external generative organs have at first the same appearance in the two sexes, and consist of a swelling, the genital eminence, in the ventral wall of the cloaca. This in the male becomes the penis and in the female the clitoris. Throughout the generative system the male organs depart most from the undifferentiated type, and in the case of the genital eminence two folds grow together and enclose the urogenital passage, thus making the urethra perforate the penis, while in the female these two folds remain separate as the labia minora or nymphae. Sometimes in the male the folds fail to unite completely, and then there is an opening into the urethra on the under surface of the penisa condition known as hypospadias. In the undifferentiated condition the integument surrounding the genital opening is raised into a horseshoelike swelling with its convexity over the pubic symphysis and its concavity to-ward the anus; the lateral parts of this remain separate in the female and form the labia majora, but in the male they unite to form the scrotum. The median part forms the mons Veneris or mons Jovis. The Descent of the Testis.It has been shown that the testis is formed in the loin region of the embryo close to the kidney, and it is only in the later months of foetal life that it changes this position for that of the scrotum. In the lower part of the genital ridge a fibro-muscular cord is formed which stretches from the lower part of the testis to the bottom of the scrotum; it is known as the gubernaculum testis, and by its means the testis is directed into the scrotum. Before the testis descends, a pouch of peritoneum called the processus vaginalis passes down in front of the gubernaculum through the opening in the abdominal wall, which afterwards becomes the inguinal canal, into the scrotum, and behind this the testis descends, carrying with it the mesonephros and mesonephric duct. These, as has already been pointed out, form the epididymis and vas deferens. At the sixth
In the female the ovary undergoes a descent like that of the testis, but it is less marked owing to the fact that the gubernaculum becomes attached to the Mullerian duct where that duct joins its fellow to form the uterus; hence the ovary does not descend lower than the level of the top of the uterus, and the part of the gubernaculum running between it and the uterus remains as the ligament of the ovary, while the part running from the uterus to the labium is the round ligament. In rare cases the ovary may be drawn into the labium just as the testis is drawn into the scrotum. Comparative Anatomy.In the Urochorda, the class to which Salpa, Pyrosoma and the sea squirts (Ascidians) belong, male and female generative glands (gonads) are present in the same individual; they are therefore hermaphrodite. In the Acrania (Amphioxus) there are some twenty-six pairs of gonads arranged segmentally along the side of the pharynx and intestine and bulging into the atrium. Between them and the atrial wall, however, is a rudimentary. remnant of the coelom, through which the spermatozoa or ova (for the sexes are distinct) burst into the atrial cavity. There are no genital ducts. In the Cyclostomata (lampreys and hags) only one median gonad is found, and its contents (spermatozoa or ova) burst into the coelom and then pass through the genital pores into the urogenital sinus and so to the exterior. It is probable that the single gonad is accounted for by the fact that its fellow has been suppressed. In the Elasmobranchs or cartilaginous fishes there are usually two testes or two ovaries, though in the dogfish one of the latter is suppressed. From each testis, which in fish is popularly known as the soft roe, vasa efferentia lead into the mesonephros, and the semen is conducted down the vas deferens or mesonephric duct into the urogenital sinus, into which also the ureters open. Sometimes one or more thin-walled diverticulathe sperm sacsopen close to the aperture of the vas deferens. In the female the ova are large, on account of the quantity of yolk, and they burst into the coelum, from which they pass into the large Mullerian ducts or oviducts. In the oviparous forms, such as the common dogfish (Scyllium), there is an oviducal gland which secretes a horny case for the egg after it is fertilized, and these cases have various shapes in different species. Some of the Elasmobranchs, e.g., the spiny dogfish (Acanthias), are viviparous, and in these the lower part of the oviduct is enlarged and acts as a uterus. In male elasmobranchs the anterior part of the Mullerian duct persists. Paired intromittent organs (claspers) are developed on the pelvic fins of the males; these conduct the semen into the cloaca of the female. In the teleostean and ganoid fishes (Teleostomi) the nephridial ducts are not always used as genital ducts, but special coelomic ducts are formed (see COELOM and SEROUS MEMBRANES). In the Dipnoi or mudfish long coiled Miillerian ducts are present, but the testes either pour their secretion directly into the coelom or, as in Protopterus, have ducts which are probably coelomic in origin. In both the Teleostomi and Dipnoi the testes and ovaries are paired. True hermaphroditism is known among fishes, the hag (Myxine) and the sea perch (Serranus) being examples. In many others it occurs as an abnormality. In the Amphibia both ovaries and testes are symmetrical. In the snakelike forms which are found in the order Gymnophiona the testes are a series of separate lobules extending for a long distance, one behind the other, and joined by a connecting duct from which vasa efferentia pass into the Malpighian capsules of the kidneys, and so the sperm is conducted to the mesonephric duct, which acts both as vas deferens and ureter. The Mallerian ducts or oviducts are long and often coiled in Amphibia, and usually open separately into the cloaca. There is no penis, but in certain forms, especially the Gymnophiona, the cloaca is protrusible in the male and acts as an intromittent organ. Corpora adiposa or fat bodies are present in all Amphibians, and probably nourish the sexual cells during the hibernating period. In Reptilia two testes and ovaries are developed, though they are often asymmetrical in position. In Lizards the vas deferens and ureter open into the cloaca by a common orifice; as they do in the human embryo. In these animals there are two penes, which can be protruded and retracted through the vent; but in the higher reptiles (Chelonia and Crocodilia) there is a single median penis rising from the ventral wall of the cloaca, composed of erectile tissue and deeply grooved on its dorsal surface for the passage of the sperm. In birds the right ovary and oviduct degenerates, and the left alone is functional. In the male the ureter and vas deferens open separately into the cloaca, and in the Ratitae (ostriches) and Anseres (ducks and geese) a well-developed penis is present in the male. In the ostrich this is fibrous, and bifurcated at its base, suggesting the crura penis of higher forms. Among the Mammalia the Monotremata (Ornithorhynchus and Echidna) have bird-like affinities. The left ovary is larger than the right, and the oviducts open separately into the cloaca and do not fuse to form a uterus. The testes retain their abdominal position; and the vasa deferentia open into the base of the penis, which lies in a separate sheath in the ventral wall of the cloaca, and shows an advance on that of the reptiles and birds in that the groove is now converted into a complete tunnel. In the female there is a well-developed clitoris, having the same relations as the penis. In the marsupials the cloaca is very short, and the vagina and rectum open separately into it. The two uteri open separately and three vaginae are formed, two lateral and one median. The two lateral join together below to form a single median lower vagina, and it is by means of these that the spermatozoa pass up into the oviducts. The upper median vagina at first does not open into the lower one, but during parturition a communication is established which in some animals remains permanent (see J. P. Hill, Proc. Linn. Soc. N.S. Wales, 1899 and 1900). This tripartite arrangement of the upper part of the marsupial vagina is of especial interest
When, as in marsur ials, the two uteri open separately into the vagina by two ora, the arrangement is spoken of as uterus duplex. When the two uteri join below and open by one os externum, it is known as uterus bipartitus. When the uterus bifurcates above and has two horns for the reception of the Fallopian tubes (oviducts), but is otherwise single, the term uterus bicornis is given to it, while the single uterus of man and other Primates is called uterus simplex. From the marsupials upward theovarian end of the Fallopian tube has the characteristic fimbriated appearance noticed in human anatomy. In some mammals, such as the sow and the cow, the Wolffian duct is persistent in the female and runs along the side of the vagina as the duct of Gartner. It is possible that the lateral vaginae of the marsupials are of Wolffian origin. In marsupials the testes descend into the scrotum, which lies in these animals in front of instead of behind the penis. In some mammals, such as the elephant, they never reach the scrotum at all; while in others, e.g. many rodents, they can be drawn up into the abdomen or lowered into the scrotum. The subject of the descent of the testicles has been very fully treated by H. Klaatsche, " Ueber den Descensus testiculorum," Morph. Jahrb., Bd. xvi. The prostate is met with in its most simple forms in marsupials, in which it is a mere thickening of the mucous membrane of the urethra; in the sheep it forms a bilateral elongated mass of gland tissue lying behind the urethra and surrounded by a well-developed layer of striped muscle. In the sloth it is said to be altogether absent, while in many of the insectivores and rodents it consists of many lobes which usually show a bilateral arrangement. The vesiculae seminales are usually present in the Eutheria or higher mammals, and sometimes, as in the hedge-hog, are very large, though they are absent in the Carnivora. Cowper's glands are usually present and functional throughout From C. S. Wallace's Prostatic Enlargement. life. The uterus masculinus is also usually present, but there is grave doubt whether the large organ called by this name in the rabbit should not rather be regarded as homologous with part of the vesiculae seminales. The penis shows many diversities of arrangement; above the marsupials its two crura obtain an attachment to the ischium. In many mammals it is quite hidden by the skin in the flaccid condition, and its external orifice may range from the perineum in the marsupials to the middle of the ventral wall of the abdomen in the ruminants. In the Marsupialia, Rodentia, Chiroptera, Carnivora and some Primates an os penis is developed in connexion with the corpora cavernosa. The clitoris is present in all mammals; sometimes, as in the female" hyena, it is very large, and at others, as in the lemur, it is perforated by the urethra. For further details and literature, see Oppel's Lehrbuch der vergleich. mikroskop. Anatomie der Wirbelthiere, Bd. iv. (Jena, 1904) ; also Gegenbaur's Vergleich. Anat. der Wirbelthiere, and Wiedersheim's Comparative Anatomy of Vertebrates, translated by W. N. Parker (London, 1907). (F. G. P.) End of Article: REPRODUCTIVE SYSTEM, IN ANATOMY If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/RAY_RHU/REPRODUCTIVE_SYSTEM_IN_ANATOMY.html"> REPRODUCTIVE SYSTEM, IN ANATOMY </a> |
|
|
(Previous) REPRODUCTION OF |
(Next) REPSOLD, JOHANN GEORG (17711830) |
Jesus Christ Saves Ministries, P.O. Box 70696, Pasadena, CA 91117JCSM is a 501(c)(3), non-profit organization. Copyright © 1997-present. |
Free & Cheap Cell
Phones |
Cheap Long Distance
Phone Service Carriers |
Talk America Local Phone Service
|
Ztel & MCI - Unlimited Long Distance
Compare
Cell Phone Plans & Companies |
International Calling Cards & Prepaid Phone Cards |
Voice Over IP Broadband Internet Phone
Service | Wireless
Phone Plans & Cheap Cell Phones
|
_____________________________________________________________________________
