1904.] AX ATOMY OF CERTAIN SXAKES. Ill 



two arrangements of the intercostals, the Boine or the Pythonine, 

 is the more primitive ; perhaps it is the former. In any case it 

 is from the Boine rather than the P}-thonine type that the inter- 

 costal system of many Colubrine Sex'pents is deriyable. 



Eryx co/iicus differs in detail from^ Eryx jaculus in the arrange- 

 ment of the intercostal arteries. Anteriorly, the ai-teries are 

 giyen off singly and regulai-ly, bifm^cating just before their entry 

 into the thickness of the parietes. There is with great regularity 

 one to each vertebra. The only excej)tion that I noticed was in 

 the case of one intercostal arising from the right aorta in front 

 of the junction of the two aortae, and of another some way behind ; 

 these supplied two intervertebral spaces. This apparently is the 

 only trace left anteriorly of the arrangement characterising 

 Eryx jaculus. Far back, much further than in E. jaculus, the 

 paired arrangement of the intercostals is seen. Still it is evident 

 that the two species do not differ in the type of the arrangement 

 of the intercostals. 



Eryx johni again shows a fundamental likeness to, but detailed 

 differences from, the other two species of the genus. The general 

 agreement is that the anterior series of intercostals arise singly 

 from the aorta and bifurcate only just before entering the parietes. 

 They begin to be double in origin shortly behind the Hver. In 

 the region where they are double they are frequently asymmetrical 

 in both size and in point of origin from the aorta. Thirteen 

 intercostals arise from the right aortic arch before its union 

 with the left. There is no trace of any formation of an azygos 

 median vertebral artery such as occurs in Eryx jaculus. The 

 intercostal system of this species in fact is somewhat intermediate 

 between those of the two other species of the genus. 



§ Some Visceral Arteries. 



(Esophageal arteries. — I have examined these arteries carefully 



in an injected example of Eryx ja-culus. It agrees with other 

 snakes and with the Lacei-tilia in the fact that the intercostals 

 (ah-eady described on p. 109) arise from the right aoi^tic arch 

 only. On the other hand, branches to the cesophagus, which are 

 represented in the drawing (text-fig. 19, p. 109), arise either 

 directly or indirectly from both arches, I have not observed 

 this double origin of the cesophageal branches in any other 

 Ophidian ; but, as I am not quite in a position to deny its 

 occurrence, I cannot emphasise the fact as a characteristic of the 

 Boidas. It is, however, 1 am inclined to think, an anatomical 

 feature not found in the Lacertilia. The oesophageal vessels, or 

 rather vessel (for I only noticed one), arises from the left aorta ; 

 it passes back along the cesophagus, giving off branches to that 

 gut, and becomes continuous with the first of the oesophageal 

 arteries arising from the conjoined aortse. The right aoita does 

 not directly give off oesophageal arteries. But from two of the 

 intercostals of the right aortic arch such arteries arise. 



