ANATOMY ANJ PHYSIOLYGY OF THE HORSE. 



123 



alongside of the venous trunks ; and not 

 infrequently may be filled by introducing 

 mercury into the spermatic artery, c. The 

 VAS DEFERENS, though a constituent of the 

 cord, takes at first a solitary course, remote 

 from the blood vessels. The duct issues 

 from the summit of the head of the epidi- 

 dymis, beginning in a series of convolu- 

 tions gradually unwinding as it proceeds ; 

 it takes an obfique course nearly as high as 

 the external ring, where it joins the blood 

 vessels, and continues to accompany them 

 posteriorly through the inguinal canal : at 

 the internal ring it leaves them, turns 

 inward and ascends into the pelvis, where 

 we find it creeping along the side of the 

 bladder infolded in peritoneum to get to the 

 cervix, crossing under its course first the 

 umbilical artery and then the ureter; at 

 length it terminates by rather a contracted 

 orifice within the mouth of the duct of the 

 vesicula seminalis, just behind a little emi- 

 nence in the urethra — the capat g-alinag-inis, 

 about an inch posteriorly to the cervix of 

 the bladder. Within the inguinal passage 

 the duct is accompanied by the artery of 

 the vas deferens,^ long slender branch of the 

 epigastric. Its canal, flexuous until the 

 duct has joined the cord, but straight in its 

 subsequent course, is not uniform through- 

 out in caliber ; the area of its tortuous part 

 is large, but as it becomes straight it grows 

 contracted : having entered the pelvis, it 

 gradually enlarges again, and acquires un- 

 usual volume in running along the side of the 

 bladder ; and the canal of the enlarged por- 

 tion presents a riticulated structure, which 

 gives its exterior an irregular, tuberculated 

 appearance ; the most contracted part is 

 that in union with the duct of the vesicula 

 seminalis, which is a comparatively small 

 cylindrical conduit. The parietes of the 

 duct are so remarkably thick and firm to 

 the feel, that we distinguish it at once by 

 the fingers from the other parts of the 

 cord : they consist of tw^o tunics ; the ex- 

 ternal one (in which its main thickness con- 

 sists) is white, fibrous, and approaches in 

 appearance to cartilage ; the internal one is 

 thin and fine in texture, muco-membranous 



in its nature, and here and there incloses a 

 reticulated structure. The different consti- 

 tuent parts of the cord are connected alto- 

 gether by cellular substance, destitute of 

 any fat ; and from the circumstance of the 

 parts in general being more bulimy below the 

 ring, the cord increases in breadth and 

 thickness as it approaches the testicle. 



THE EPIDIDYMIS. 



The epididymis is extended along the su- 

 perior border of the testicle, upon which it 

 rests, and to wliich it is connected by the 

 tunica vaginalis reflexa. Its ends are bulky 

 in comparison to its middle : that receiving 

 the vasa efterentia, the smaller one, is the 

 caput or globus minor; the other, giving 

 rise to the vas deferens, is the globus major, 

 the part farriers call the 7iut. The interior 

 of this appendage to the testicle exhibits a 

 structure entirely vascular. The vasa ef- 

 ferentia unite and re-unite until they form 

 a single duct, of whose numberless and 

 very remarkable convolutions the globus 

 major is entirely constituted : these tortu- 

 osities (which, when squeezed, freely emit 

 semen) wiU admit of being unwound for a 

 considerable extent, so as to have the 

 length of the duct calculated with very 

 tolerable exactness from beginning to end, 

 which has been found to amount to several 

 yards. It is small at its formation, but grows 

 imperceptibly larger in making its manifold 

 windings and turnings, until at length it 

 assumes the size of the vas deferens, in 

 which it ends. Its various convolutions are 

 connected together by cellular membrane, 

 and are interspersed with a sparing supply 

 of blood vessels. 



The course of the semen is this: It is 

 secreted by the capillary coils of the sper- 

 matic artery, from which it is received by 

 the tubili seminiferi: these tubes carry it 

 into the rete, and the rete discharges it 

 through the vasa efferentia into the epididy- 

 mis, from which it is conducted by the 

 vas deferens into the urethra. 



Formation and Descent. — It is a singu- 

 lar fact, that the organs whose structures 

 we have been investigating, are originally 



