Anatomy of Eryx and other Boidae. 235 



existence of only a single renal artery on each side in some 

 Boidie, though doubtless associated with a small kidney *, is 

 of itself, as it appears to me, a primitive character, inasmuch 

 as there is here an absence of reduplication, so common a 

 feature of the vascular and other systems in the Ophidia. 



The same arguments may be used in the case of the gastric 

 arteries, which are two in Eryx and three in Python spilotes. 

 In the genus Coluber there may be as many as ten or eleven 

 gastric arteries. 



It is not common in snakes, so far as my experience goes, 

 for the two carotids at their origin to be equal in size : they 

 are, however, in both Eryx jaculus and E. conicus, but not 

 in Python spilotes. Another primitive (?) feature which is 

 found in only one of the two genera mentioned is connected 

 with the dorsal musculature of Python spilotes. As a general 

 rule, in snakes a beautiful complex of tendons is seen to 

 occupy the dorsal median region when the animal is opened 

 from below. In Python this region is much less converted 

 into tendon ; it remains muscular. Now there is evidence 

 elsewhere in the animal kingdom of muscles becoming more 

 tendinous or being converted entirely into ligaments, but not 

 of ligaments and tendons acquiring a muscular character f. 



Some features in the circulatory system, other than those 

 briefly referred to above, are not without interest. 



It is at least rare among snakes | for the arteries supplying 

 the gonads to arise from the aorta opposite to eacli other 

 instead of one being in front of the other. Nevertheless, in 

 a female Eryx conicus the ovarian arteries form a pair arising 

 side by side. As is usual, these arteries immediately follow 

 the superior mesenteric. 



It is a peculiarity of snakes, contrasted with lizards, that 

 the anterior abdominal vein of the latter is single, while it is 

 at least sometimes partly double in the Ophidia. This point 

 of difference from the Lacertilia, and, so far, of resemblance 

 to the Crocodilia, is apt to be slurred over in text-books. In 

 one specimen of Eryx conicus the vessel was single through- 

 out ; in another it was partly double, as was the case with 

 two specimens of Eryx jaculus. In Boa constrictor the vessel 

 was single for a distance of six inches behind the gall-bladder 

 and thence to the cloaca double. 



* In Heterodon plcttyrhinus, for example, the proportions between the 

 length of the body (to the vent) and the length of the larger kidney are 

 9 : 1, in Boa constrictor 15 : 1. 



f For example, one of the glutaeal muscles in hornbills. 



\ I have not myself observed a single instance, except in the case 

 mentioned above. 



