THORAX AND ABDOMEN OF THE HORSE 



73 



The disposition of the visceral portion of the tunica vaginalis should 

 now receive attention. Applied to the surface of the testis and 

 epididymis, it gives these organs their smooth appearance and 

 lines a cavity, the sinus epididymidis, between them. Note that 

 the entrance to this cavity is lateral in position. Leaving the dorsal 

 border of the epididymis, the vaginal tunic forms an investment for the 

 spermatic cord. 



The continuity of the visceral and parietal parts of the tunica 

 vaoinalis is alonff the caudal border of the scrotum and over the liga- 

 ment of the epididymis. 



Pampiniform plexus 



Caput epididymidis 



Ductus deferens. 

 Tunica vaginalis. 



Testis ^ 



Cauda epididymidis. 



Fig. 31. — Medial aspect of the right testis and epididymis. 



Descent of the testis (Descensus testis). — The characteristic dis- 

 position of the spermatic cord, and the fact that the blood-supply of the 

 testis is derived from a considerable distance, will be understood if it is 

 remembered that the testis does not develop in the scrotum, nor does it 

 arrive in that sac until the end of intra-uterine life. The testis develops 

 in the sublumbar region ventral to the position assumed by the per- 

 manent kidney. Here, in the embryo, it is held in position by a short 

 mesenterial fold of peritoneum, the mesorchium,^ containing blood 

 vessels and nerves. 



The scrotum is formed by a diverticulum of the abdominal wall, into 

 which, about the middle of intra-uterine life, a blind pouch of peri- 

 toneum — the processus vaginalis — is protruded. Into this diverticulum 

 the testis with its mesorchium descends. How far the descent of the 

 testis is governed by a muscular and fibrous cord, the gubernaculum - 



' M^ffos (raesos) [Gr.], middle ; 6pxis (orchis) [Gr.], the testis. 

 - Chibernaculum [L.], a governor or guide ; gubernare [L.], to govern, steer, or 

 pilot. 



