Part 153

THE ADRENALS

The =right adrenal= lies between the anterior part of the inner border of the kidney and the posterior vena cava. It is somewhat prismatic, and is pointed at either end.

The =left adrenal= lies along the posterior aorta, from the renal vein forward, but is not in contact with the kidney. It is elongated and flattened dorso-ventrally. (There is a furrow on the ventral surface for the vein which crosses it; the part in front of this furrow is discoid, and may be taken for the entire organ in a fat subject.)

The cortex is pale yellow in color, the medulla dark brown.

THE MALE GENITAL ORGANS

The male =genital organs= (Organa genitalia masculina) are: (1) The two =testicles=, the essential reproductive glands, with their coverings and appendages; (2) the =vasa deferentia=, the ducts of the testicles; (3) the =vesiculæ seminales=; (4) the =prostate=, a musculo-glandular organ; (5) the two =bulbo-urethral= (or Cowper’s) =glands=; (6) the male =urethra=, a canal which transmits the generative and urinary secretions; (7) the =penis=, the male copulatory organ. The vesiculæ seminales, the prostate, and the bulbo-urethral glands discharge their secretions into the urethra, where they mix with the seminal fluid secreted by the testicles; hence they are often termed the accessory sexual glands.

MALE GENITAL ORGANS OF THE HORSE

THE TESTICLES

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.

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.

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.) ]

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=. 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.