VOL. XXIV.] PHILOSOPHICAL TKANSACTIONS. 113 



press the epididymides and vasa deferentia, and oblige them to dispatch their 

 contents (the semen) into the urethra in the time of the coition, which other- 

 wise would have a slow progress; but this contrivance appears more peculiarly 

 requisite to this animal, because the defect of the vesiculae seminales here seem 

 to be supplied by the largeness of the epididymides of the testes ww, fig. 2, 3, 

 which are the excretory ducts of the testes, and appear in this animal to have a 

 larger bore than ordinary: for this reason, the tunicas vaginales are very straight 

 in this animal, as appears in the figure tvrr, fig. 2. 



On discovering the originations of the spermatic arteries, I was surprised to 

 meet with an appearance I never heard of, nor observed before ; and in this I 

 should not have had any satisfaction, if I had not first injected wax into the 

 trunks of the great artery iii, fig. 2, and vena cava h below the diaphragm. It 

 seems, the descending trunk, of the great artery, below the emulgent arteries, in 

 this animal, is placed directly under the trunk of the vena cava; nor does the 

 iliac branches of the arteries here twine about those of the veins, as in hu- 

 man bodies and some quadrupeds, which is done perhaps to compress the 

 channels of the veins, by means of the pulsation of these arteries, to drive 

 up the blood in the veins towards the heart; but that contrivance seems no way 

 necessary in this animal, because the contrary position of its body is more 

 customary, in hanging by its tail with its head downwards: it is not unlikely, if 

 the veins of this animal were examined below the heart, but we should meet 

 with some contrivance to prevent the precipitate flux of the blood in that pen- 

 dulous position, as I have observed in the trunk of the cava immediately above 

 the liver in dogs. 



The spermatic arteries, aa, (fig. 2) arise from the forepart of the descendingtrunk 

 of the great artery, and pass through a very small perforation, made on purpose in 

 the vena cava, and descend straight to the testes, as in human bodies, and are 

 not contorted in their progress, as we find them in most, if not all quadrupeds. 

 Perhaps this perforation of the cava was not only made for transmitting the 

 spermatic arteries, but may also frame an anulus, that may check the velocity 

 which the blood would otherwise have in those arteries, which rapid motion of 

 the blood we find nature studiously avoids in the testes of all animals : for in 

 men we see these spermatic arteries (contrary to all other trunks of arteries) are 

 less at their originations from the great artery ; and in quadrupeds (except in 

 this) the spermatic arteries are contorted before they reach the testes. The 

 spermatic veins, after leaving the testes of this animal (like those of human 

 bodies) have several divisions and inosculations, which are all reduced to one 

 trunk on each side, and empty themselves into the cava immediately above the 

 perforation bb. ,.^ri /sj;.' » ' » -; 



VOL. v. Q, 



