146 EQUINE ANATOMY. 



it is thickened, and called the corpus highmorianum or mediasti- 

 num testis: through this the seminal tubules pass from the in- 

 terior. 



The tubules are divided into groups or lobules, about 200 or 300 

 in number, each lobule being found between prolongations of the 

 fibrous tunic, and about one or two yards in length. 



The tubules are about -^Q- of an inch in diameter; have a base- 

 ment membrane, covered by several layers of epithelium, which 

 fill the tube, spermatozoids being found in the lumen. 



The lobuli testis consists simply of these tubes much convoluted; 

 passing through the mediastinum, they unite in about twenty tubes 

 the vasa recta; forming a network, the rete testis, and are con- 

 tinued into the epididymis and the vasa efjerentia. 



THE EPIDIDYMIS. 



The epididymis is an elongated body lying on top of the tes- 

 ticle, and composed of the seminal duct, much convoluted, the 

 vasa efferentia uniting to form it at its anterior portion the head, 

 or globus major. The posterior extremity, or tail, is called the 

 globus minor. Between the globi is the body. The seminal duct, 

 or vas deferens, is continuous with the globus minor. 



Structure. 



Externally a circular and longitudinal muscular layer, with 

 fibrous covering, covered by a mucous membrane lined with 

 ciliated epithelium. 



Arteries. 



Spermatic, from the aorta. 



Veins are markedly spread out on the cord, the pampiniform 

 plexus, which finally empties into the posterior cava. 



Nerves. 



From sympathetic. 



Descent of the Testis. 



The testicle remains in the abdominal cavity, in the sub-lumbar 

 region, till after birth, usually reaching the scrotum at the age of 

 six months. The active part in the descent is taken by the guber- 

 naculum testis, a fibrous cord continuous below with the dartos 

 and ending above in the abdominal cavity. It pulls the testis down- 

 ward, carrying the peritoneum before it, which becomes inverted 

 over it, forming the tunica vaginalis. The portion at the upper 



