146 EQUINE ANATOMY. 



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

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

 terior. 



T/ie tubules are divided into groups ox 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 2-^-^ 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 efferentia. 



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 eiferentia uniting to form it at its anterior portion — the head, 

 or globus 7Jiajor. The posterior extremity, or tail, is called the 

 globus 7ninor. 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 

 gubernaculmn testis, a fibrous cord continuous below with the 

 dartos and ending above in the abdominal cavity. It pulls the 

 testis downward, carrying the peritoneum before it, which becomes 

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



