490 



THE MALE GENITAL ORGANS OF THE HORSE 



Like the abdominal ]:)eritoneuin, 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 jjart 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 j^eritoneal cavity, with which it communicates 

 through the vaginal ring (Annulus vaginalis). It contains normally a small quan- 

 tity 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 



Spermatic vessels and nerves 



Parietal layer of tunica ._ 

 vaginalis 



Visceral layer of tunica 

 vaginalis or mesorchium 



Cremaster internus 

 Vas deferens 



Fig. .39.3. 



-Dia<;ram of Cross-section of Spermatic Cord and Tunica Vaginalis; Lattkr Rf.preskntkd as 



Distended. 



only be applied to the abdominal opening of the canal, the subperitoneal ring. Tlic peritoneal 

 ring at which the cavity of the tunica vaginalis opens into the general peritoneal sac is (hstin- 

 guished by tlie naiiic vaginal ring. It is i)laccd about four or five inches (ca. 10 to 12 cm.) from 

 the linca alba, and about two or three inclies (ca. (i to <S cm.) in front of the ilio-pectineal eminence. 

 In stallions it will usually admit the end of the finger readily, l)ut 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. 



DESCENT OF THE TESTICLES 

 During early foetal 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 ])roce(vls it gradually migrates from this primitive position, and finally 

 passes down tlie 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 tisstie and unstrii)ed muscle. One of these cords is short 

 and connects the tail of the epididymis with the testicle; later it becomes shorter, 



