488 THE MALE GENITAL ORGANS OF THE HORSE 



one testicle — more often the left — is the larger and more dependent. It varies 

 in fosm and appearance in the same subject, according to the condition of its sub- 

 cutaneous 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 verj^ large sebaceous and sweat glands. It is marked centrally by a longitu- 

 dinal furrow, in which is a line, the raphe 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 raphe 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. 



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 ftrst 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 al^domen at the internal 

 inguinal ring. It is thin above, but is thick in its scrotal part, where it is strength- 

 ened by fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It 

 will ])e described further under the caption tunica vaginalis.' 



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 de- 

 tached 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 ])elvic 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 l)ladder) it leaves the edge of the fold 

 and inclin(»s inward l)etween 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 bj^ the necks of the vesicuhc 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 



' This is a remnant of the gubernaculum testis of the foetus. 



- The tunica vaginalis is not a part of the scrotum in the strict or narrow sense of that term, 

 but is included here on practical grounds. 



