Part 52

The =testicles= (Testes) are situated in the inguinal region, inclosed in a diverticulum of the abdomen termed the scrotum. Their long axes are nearly longitudinal. They are ovoid in form, but considerably compressed from side to side. Each presents two surfaces, two borders, and two extremities. The =internal= and =external surfaces= (Facies medialis, lateralis) are convex and smooth. The =free= or ventral =border= (Margo liber) is convex in both directions. The =attached= or dorsal =border= (Margo epididymidis) is nearly straight, and is the one by which the gland is suspended in the scrotum by the spermatic cord; the epididymis is attached to this border and overlies it externally. The =anterior= and =posterior extremities= (Extremitas capitata, caudalis) are rounded.

At the anterior extremity there is often a sessile or pedunculated sac which contains a clear fluid; this is the =appendix testis= or hydatid of Morgagni, from which a thread-like process extends backward toward the vas deferens. It is regarded as a remnant of the Müllerian duct of the embryo.

A testicle of average size of an adult stallion is about four or five inches (ca. 10 to 12 cm.) long, two and a half inches (ca. 6 to 7 cm.) high, and one and a half to two inches (ca. 4 to 5 cm.) wide; it weighs about ten and one-half ounces (ca. 300 grams). They vary much in size in different subjects, and are commonly of unequal size, the left one being more often the larger.

The =epididymis= is adherent to the attached border of the testicle, and overlaps somewhat the external surface. Its anterior enlarged end is termed the =head= or globus major (Caput epididymidis), and its posterior, slightly enlarged end is the tail or globus minor (Cauda epididymidis); while the intermediate narrow part is the =body= (Corpus epididymidis). The head is closely connected with the testicle by the efferent ducts of the latter, by connective tissue, and by the serous membrane. The body is less closely attached by the serous covering, which forms externally a pocket beneath the epididymis termed the =digital fossa= (Sinus epididymidis). The tail is firmly attached to the posterior extremity of the testicle by a short ligament (Lig. epididymidis), formed by a thick fold of the tunica vaginalis, which contains smooth muscle-fibers; it is continued by the vas deferens.

=Structure of the Testicle and Epididymis.= The greater part of the surface of the testicle is covered by a serous membrane, the =tunica vaginalis propria=, which is the visceral layer of the serous envelop of the cord and testicle; this is reflected from the attached border of the gland, leaving an uncovered area at which the vessels and nerves in the spermatic cord reach the testicle. Beneath this serous covering is the =tunica albuginea=, a strong capsule composed of dense white inelastic fibrous tissue and unstriped muscle-fibers. From the deep surface of this tunic delicate membranous =septa= (Septula testis) pass into the gland, dividing it into pyramidal spaces, the bases of which are peripheral. At the anterior part of the attached border of the testicle connective tissue and smooth muscle-fibers pass into the substance of the gland, forming the =mediastinum testis=; from this the septa radiate. The mediastinum contains a network of fine canals, the =rete testis=; it is traversed by blood-vessels, which radiate on the septa to the deep face of the tunica albuginea, forming a delicate network—the so-called tunica vasculosa. The spaces imperfectly marked off by the septa contain the =parenchyma testis=, which consists of =seminiferous tubules= (Tubuli seminiferi), supported by loose intertubular connective tissue. The tubules are collected into small masses or =lobules= (Lobuli testis). They are at first very tortuous (Tubuli contorti); toward the apex of the lobule they unite with other tubules, forming larger straight tubules (Tubuli recti); these pass into the mediastinum testis, where they form the =rete testis=. From the latter a number (ca. 15 to 20) of larger =efferent tubules= (Vasa efferentia) pierce the albuginea and enter the head of the epididymis.

[Illustration:

FIG. 390.—INGUINAL REGION OF STALLION, WITH TESTICLES EXPOSED.

_a_, _a′_, Testicles; _b_, scrotum, opened and reflected; _c_, tunica vaginalis communis, opened and reflected; _d_, ligament of epididymis; _e_, tunica vaginalis propria (mesorchium); _f_, vas deferens; _g_, _g′_, tail of epididymis; _h_, body of same; _i_, head of same; _k_, digital fossa or sinus epididymidis; _l_, spermatic vessels showing through tunica vaginalis propria; _m_, spermatic artery; _n_, prepuce; _n′_, raphé; _o_, preputial orifice. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) ]

The =epididymis= is covered by the tunica vaginalis propria and a thin albuginea. Its head consists of =lobules= (Lobuli epididymidis), each of which consists of a coiled tubule or =conus vasculosus=, which succeeds a vas efferens. By the union of these tubules is formed a single tube, the =duct of the epididymis= (Ductus epididymidis), which, by its complex coils, forms the body and tail of the epididymis and terminates in the vas deferens. The tubules and the coils of the duct of the epididymis are held together by connective tissue and unstriped muscle-fibers. The tubules and duct are lined with ciliated epithelium, and the duct has a muscular coat which consists of longitudinal and circular fibers.

=Vessels and Nerves.=—The testicle is richly supplied with blood by the =spermatic artery=, a branch of the posterior aorta. The artery descends in the anterior part of the spermatic cord, and is very tortuous near the testicle; on reaching the attached border of the gland it passes backward in a flexuous manner, giving branches to the testicle and epididymis, turns around the posterior extremity, and runs forward on the free border to the anterior extremity. It is partially embedded in the tunica albuginea, and detaches lateral branches which ascend in a tortuous fashion on each surface of the testicle; these give off small branches which enter the gland on the septa.

[Illustration:

FIG. 391.—RIGHT TESTICLE AND SPERMATIC CORD OF HORSE, INCLOSED IN TUNICA VAGINALIS.

_c_, Tunica vaginalis communis; _g_, prominence caused by tail of epididymis; _p_, cremaster externus muscle. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) ]

[Illustration:

FIG. 392.—RIGHT TESTICLE AND SPERMATIC CORD OF HORSE, EXPOSED.

_a′_, External surface of testicle; _c_, tunica vaginalis, cut and reflected; _d_, ligament of epididymis; _e_, mesorchium; _g_, tail, _h_, body, _i_, head of epididymis; _k_, digital fossa or sinus epididymidis; _l_, spermatic vessels showing through tunica vaginalis propria; _m_, end of spermatic artery. Dotted line indicates position of vas deferens on other side of mesorchium. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) ]

The =spermatic veins= on leaving the testicle, form the =pampiniform plexus= around the artery in the spermatic cord. The vein which issues from this plexus usually joins the posterior vena cava on the right side, the left renal vein on the left side.

The =nerves=, derived from the renal and posterior mesenteric plexuses, form the =spermatic plexus= around the vessels.

THE SCROTUM

The =scrotum=, in which the testicles and the lower parts of the spermatic cords are situated, is somewhat globular in form, but is commonly asymmetrical, since one testicle—more often the left—is the larger and more dependent. It varies in form and appearance in the same subject, according to the condition of its subcutaneous muscular tissue. The latter contracts on exposure to cold, so that the scrotum is drawn up and becomes thicker and wrinkled; when relaxed under the influence of heat or fatigue, or from debility, it becomes smooth and pendulous, with a constriction or neck superiorly. It consists of layers which correspond with those of the abdominal wall; considered from without inward these are:

(1) The =skin=, which is thin, elastic, usually black in color, and smooth and oily to the touch. It presents scattered short fine hairs, and is abundantly supplied with very large sebaceous and sweat glands. It is marked centrally by a longitudinal furrow, in which is a line, the =raphé scroti=; this is continued forward on the prepuce and behind on the perineum.

(2) The =dartos= (Tunica dartos) is reddish in color and is closely adherent to the skin except superiorly. It consists of fibro-elastic tissue and unstriped muscle. Along the raphé it forms a median partition, the =septum scroti=, which divides the scrotum into two pouches. Dorsally the septum divides into two layers which diverge on either side of the penis to join the abdominal tunic. At the bottom of the scrotum fibers connect the dartos closely with the tunica vaginalis and the tail of the epididymis, constituting the =scrotal ligament=.[143] Elsewhere the dartos is loosely connected with the underlying tunic by areolar tissue which contains no fat.

(3) The scrotal =fascia=, which is apparently derived from the oblique abdominal muscles.

It has been customary to describe three layers of fascia, in conformity with the accounts given in text-books of human anatomy. These are: (1) the intercolumnar or spermatic fascia, derived from the margin of the external inguinal ring; (2) the cremasteric fascia, derived from the internal oblique muscle; (3) the infundibuliform fascia, derived from the fascia transversalis. The first two cannot be distinguished by dissection and the third is (in the scrotum) fused with the parietal peritoneum of the tunica vaginalis.

(4) =The parietal layer of the tunica vaginalis.=—This is a fibro-serous sac which is continuous with the parietal peritoneum of the abdomen at the internal inguinal ring. It is thin above, but is thick in its scrotal part, where it is strengthened by fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It will be described further under the caption tunica vaginalis.[144]

THE VAS DEFERENS

This tube (Ductus deferens) extends from the tail of the epididymis to the ejaculatory duct. It passes upward in the inguinal canal, inclosed in a fold detached from the inner surface of the mesorchium, near the posterior (attached) border of the latter. At the vaginal ring it separates from the other constituents of the spermatic cord, and turns backward and inward into the pelvic cavity (Fig. 272). For some distance it lies in the free edge of the urogenital fold, by which it is attached to the lower part of the lateral wall of the pelvis. In its further course (over the dorsal surface of the bladder) it leaves the edge of the fold and inclines inward between its layers, coming in contact with the inner face of the vesicula seminalis. Over the neck of the bladder the two vasa lie very close together, flanked laterally by the necks of the vesiculæ seminales, and having the uterus masculinus between them. They then disappear under the isthmus of the prostate, and are continued through the wall of the urethra by the =ejaculatory ducts=. The latter are formed in the urethral wall by the union of the vas deferens with the duct (or neck) of the corresponding vesicula seminalis; they are thin-walled tubes, about 2 to 3 mm. long and 6 to 7 mm. wide, which open into the urethra on either side of the colliculus seminalis. In about 15 per cent. of subjects the vas deferens and duct of the seminal vesicle do not unite, but open side by side into the urethra. From its origin until it reaches the dorsal surface of the bladder the vas deferens has a uniform diameter of about a quarter of an inch (ca. 6 mm.). It then forms a fusiform dilatation, the =ampulla ductus deferentis= (Fig. 394); this part is about six to eight inches (ca. 15 to 20 cm.) long, and in its largest part nearly an inch (ca. 2 cm.) in diameter in the stallion; in geldings the dilatation is usually not very pronounced. Beyond the ampulla the duct abruptly contracts.

=Structure.=—The wall of the vas deferens is thick and the lumen relatively small, so that the tube has a firm and cord-like character. It is covered with peritoneum, except in the last few inches of its course. The loose =adventitia= contains numerous vessels and nerves. The thick =muscular coat= consists of longitudinal and circular layers. The =mucous membrane= has an epithelium of short columnar cells. In the posterior part of the tube, and especially in the ampulla, there are numerous tubulo-alveolar glands.

=Blood-supply.=—Spermatic and umbilical arteries.

=Nerve-supply.=—Spermatic and pelvic plexuses.

THE SPERMATIC CORD

The =spermatic cord= (Funiculus spermaticus) consists of the structures carried down by the testicle in its migration through the inguinal canal from the abdominal cavity to the scrotum. It begins at the internal inguinal ring, where its constituent parts come together, extends obliquely downward through the inguinal canal, passes over the side of the penis, and ends at the attached border of the testicle. It consists of the following structures:

(1) The =spermatic artery=.

(2) The =spermatic veins=, which form the pampiniform plexus around the artery.

(3) The =lymphatics=, which accompany the veins.

(4) Sympathetic =nerves=, which run with the artery.

(5) The =vas deferens=.

(6) The =internal cremaster muscle=, which consists of bundles of unstriped muscular tissue.

(7) The =visceral layer= of the =tunica vaginalis= or =mesorchium=.

The first four of these constituents are gathered into a rounded mass which forms the anterior part of the cord; they are united by connective tissue, interspersed with which are bundles of the cremaster internus. The vas deferens is situated posteriorly, inclosed in a special fold detached from the inner surface of the mesorchium; hence it is not visible externally.

The term spermatic cord is to a certain extent misleading as applied to most animals, while in man the structure is distinctly cord-like. In the horse, when the tunica vaginalis is slit open and the “cord” stretched out, the latter is seen to have the form of a wide sheet, the mesorchium, which has a thick, rounded anterior edge, the so-called “vascular part” of the cord. The posterior edge of the mesorchium is continuous with the parietal layer of the tunic; its inner surface presents posteriorly the deferential fold (Plica ductus deferentis). Between the two layers of the mesorchium are bundles of unstriped muscle (cremaster internus) and small vessels.

THE TUNICA VAGINALIS

The =tunica vaginalis= is a somewhat pyriform serous sac which extends from the internal inguinal ring through the inguinal canal to the bottom of the scrotum. Like the abdominal peritoneum, of which it is an evagination, it consists of two layers—parietal and visceral. The =parietal layer=, or =tunica vaginalis communis= (s. reflexa), lines the scrotum below; its narrow, tubular part lies in the inguinal canal and is directly continuous with the parietal peritoneum of the abdomen at the internal inguinal ring. The =cavity= of the tunica vaginalis (Cavum vaginale) is a diverticulum of the general peritoneal cavity, with which it communicates through the =vaginal ring= (Annulus vaginalis). It contains normally a small quantity of serous fluid. The parietal layer is reflected from the posterior wall of the inguinal canal around the structures of the cord, forming the =mesorchium=, a fold analogous to the mesentery of the intestine. The =visceral layer=, or =tunica vaginalis propria=, covers the spermatic cord, testicle, and epididymis.

The =external cremaster muscle= (M. cremaster externus) lies on the outer and posterior part of the tunic, to the scrotal part of which it is attached.

Confusion has arisen from the use of the term internal abdominal or inguinal ring in two senses. The term is used to designate the upper or abdominal opening of the inguinal canal, but it is also applied to the upper opening of the cavity of the tunica vaginalis. It should only be applied to the abdominal opening of the canal, the =subperitoneal ring=. The =peritoneal ring= at which the cavity of the tunica vaginalis opens into the general peritoneal sac is distinguished by the name =vaginal ring=. It is placed about four or five inches (ca. 10 to 12 cm.) from the linea alba, and about two or three inches (ca. 6 to 8 cm.) in front of the ilio-pectineal eminence. In stallions it will usually admit the end of the finger readily, but it may be abnormally large and allow a loop of bowel to enter the cavity of the tunica vaginalis. In the gelding it is smaller and sometimes partially occluded. In man the cavity is almost always obliterated early, except in its scrotal portion, thus abolishing the vaginal ring.

[Illustration:

FIG. 393.—DIAGRAM OF CROSS-SECTION OF SPERMATIC CORD AND TUNICA VAGINALIS; LATTER REPRESENTED AS DISTENDED. ]

DESCENT OF THE TESTICLES

During early fœtal life the testicle is situated against the dorsal wall of the abdominal cavity, in contact with the ventral surface of the corresponding kidney. As growth proceeds it gradually migrates from this primitive position, and finally passes down the inguinal canal into the scrotum. Previous to its descent through the abdominal wall the testicle is suspended by a fold of peritoneum, termed the =mesorchium=. This fold contains the vessels and nerves of the testicle in its anterior border. In its posterior edge is the elongated tail of the epididymis, and two cords of fibrous tissue and unstriped muscle. One of these cords is short and connects the tail of the epididymis with the testicle; later it becomes shorter, and is termed the ligament of the epididymis. The other cord, the =gubernaculum testis=, extends from the tail of the epididymis to the subperitoneal tissue in the vicinity of the future vaginal ring. The =deferential fold= (Plica ductus deferentis) is given off from the inner face of the mesorchium, and joins the urogenital fold posteriorly. The body of the epididymis at this time lies in the edge of an oblique fold formed by the outer layer of the mesorchium. After the middle of fœtal life, a pouch or diverticulum of the peritoneum, the =processus vaginalis=, grows downward through the inguinal canal, carrying with it cremaster fibers derived from the internal oblique muscle and a layer from the transversalis fascia. It is accompanied by an inguinal extension of the gubernaculum testis. The latter blends below with the subcutaneous tissue which later becomes the dartos. The tail of the epididymis first enters the processus vaginalis, followed by the testicle with its mesorchium, which descends within this diverticulum of the peritoneum until it reaches the scrotum. The vas deferens and its fold descend synchronously with the epididymis and testicle.

The mechanical factors concerned in the migration of the testicle are matters on which much uncertainty still exists. That the gubernaculum exerts sufficient traction to guide the epididymis and testicle to the inguinal canal seems plausible. The internal inguinal ring may constitute a locus minoris resistentiæ in the abdominal wall, especially after the descent of the processus vaginalis. Progressive shortening of the gubernaculum was formerly considered to be the chief cause of the descent through the abdominal wall. Increase in the intra-abdominal pressure is probably an important factor.

In the foal the descent of the testicles is often complete at birth, but it frequently happens that one testicle or both may be retained in the inguinal canal or in the abdomen for some months. In other cases the testicle may return into the canal or abdomen, since in the young foal the vaginal ring is large and the testicle small and soft, and not yet closely anchored by the scrotal ligament. In rare cases the descent may be completed as late as the fourth year (personal observation).

Indefinite retention of one testicle or both in the abdominal cavity or inguinal canal is not rare in horses; this condition is termed cryptorchism. Abdominal retention is the more usual form of cryptorchism in adult horses, inguinal retention being usually temporary. The retained testicle is usually, but not always, small, thin, soft, and flabby, and is non-spermiogenic. The processus vaginalis and the inguinal part of the gubernaculum are usually present, but may be rudimentary. The ligament of the epididymis and the corresponding part of the mesorechium are often so long that the tail of the epididymis may be several inches distant from the testicle. The abdominal part of the gubernaculum may be 8 to 10 inches (ca. 20 to 25 cm.) long, and the ligament of the epididymis much elongated (10 to 15 cm. in length according to Vennerholm); thus the testicle may have a wide range. The vaginal ring is sometimes closed.

In many mammals the testicles normally remain in the abdominal cavity; such animals are termed testiconda, and include the elephant, some insectivora, hyrax, sloths, ant-eaters, armadillos, and cetacea. In others the testicles descend periodically during the period of œstrum, and then return into the abdomen, or they may be extruded and retracted voluntarily; this is true of most rodents, many insectivora (moles, shrews, hedgehog), and bats.

THE VESICULAE SEMINALES

The =vesiculæ seminales= (Fig. 394) are two elongated and somewhat pyriform sacs, which lie on either side of the posterior part of the dorsal surface of the bladder. They are partly inclosed in the urogenital fold, and are related to the rectum dorsally. Their long axes are parallel with the vas deferentia and converge posteriorly. Each consists of a rounded blind end, the =fundus=, a middle, slightly narrower part, the =body=, and a posterior constricted part, the =neck= or =duct=.

In the stallion they are about six to eight inches (ca. 15 to 20 cm.) long, and their greatest diameter is about two inches (ca. 5 cm.); in the gelding they are usually much smaller.[145]

The vesiculæ are, for the most part, retroperitoneal, but the fundus extends forward into the urogenital fold and hence has a serous covering. The =neck= or =duct= (Ductus excretorius) dips under the prostate, and usually unites with the end of the vas deferens to form the =ejaculatory duct=.

[Illustration:

FIG. 394.—INTERNAL GENITAL ORGANS OF STALLION, DORSAL VIEW.

On left side urethral muscle has been removed over bulbo-urethral gland. Cornua of uterus masculinus are indicated in urogenital fold. ]

=Structure.=—The wall, exclusive of the partial serous coat, consists of a fibrous =adventitia=, a middle =muscular coat=, and a =mucous lining=. The muscular coat is thickest at the fundus, and consists of two planes of longitudinal fibers with a circular layer between them. The mucous membrane is thin, and is arranged in numerous folds which form a network; the spaces so inclosed present the openings of tubulo-alveolar glands. The epithelium is columnar. The =blood-supply= is derived from the =internal pudic artery=.

THE PROSTATE

The =prostate= (Prostata) is a musculo-glandular organ which lies on the neck of the bladder and the beginning of the urethra, beneath the rectum. It consists of two lateral lobes and a connecting isthmus.

The =lateral lobes=, right and left (Lobus dexter et sinister), are somewhat prismatic in form, and are directed forward, outward, and somewhat upward. The antero-internal surface of each lobe is concave and partly embraces the corresponding vesicula seminalis. The dorsal surface is concave and is in relation with the rectum. The ventral surface is convex and lies on the obturator internus muscle and fat. The apex is pointed and lies near the posterior end of the superior ischiatic spine.

The =isthmus= is a thin, transverse band, about four-fifths of an inch (ca. 2 cm.) wide. It lies over the junction of the bladder with the urethra, the uterus masculinus, the terminal parts of the vasa deferentia, and the necks of the vesiculæ seminales. Dorsally it is partly covered by transverse fibers of the urethral (Wilson’s) muscle.

=Structure.=—The prostate is inclosed in a fibro-muscular =capsule=, which sends thick, somewhat radially arranged =trabeculæ= into the gland substance, dividing it into spheroidal or ovoid =lobules=. The lobules contain a central space in which the prostatic secretion (Succus prostaticus) collects. The walls of these spaces are pouched out to form tubular diverticula, and the latter present saccular dilatations. These cavities are all lined by cubical epithelium. There are 15 to 20 =prostatic ducts= (Ductus prostatici) on either side, which perforate the urethra and open lateral to the colliculus seminalis. The =blood-supply= is derived from the =internal pudic artery=.

The surface of the prostate is commonly tuberculate in old subjects, and amyloid bodies and calcareous concretions may be found in it.

THE UTERUS MASCULINUS