36 MR. F. E. BEDDARD ON THE [Jan, 16, 



as to the partial persistence in the adult Python of the embryonic 

 umbilical vein. 



Trachea and Lung. — In this Viper the tracheal lung is not in 

 any way marked off from the ensuing thoi-aco-abdominal portion 

 of the lung. The latter extends as an efficient respiratory organ 

 for some distance down the liver. The tracheal or bronchial gutter 

 ends at a level with about the middle of the heart. There is no 

 trace of a second lung. It is necessary to emphasise these various 

 facts, since they differ among the Yiperidie. The total absence of 

 a second rudimentary lung in this species has been already noted 

 by Butler*. In addition to the species which he mentions, I may 

 note here that Lachesis gramineus has a rudimentary left lung. 

 In Ancistrodon j^iscivoriis the lung is vascular for about an inch 

 behind the heart, and the ti-acheal gutter is continued foi' about 

 the same distance, being thus moi'e extensive than in Bitis nasi- 

 cornis. In Lachesis gi'amineus the vsscn\a.r part of the lung is less 

 extensive posteriorly. Causus rhomheatus differs in some respects 

 from these other Vijoers. Like all other Solenoglypha, it possesses 

 the tracheal lung ; but it differs fi'om some other Vipers in the 

 face that the tracheal section of the lung is the only part which 

 is vascular, the rest being anangious. The trachea is continued 

 down the lung from the very beginning of the tracheal lung as a 

 gutter down to near the end of the liver. 



Intercostal Arteries. — In dealing with certain facts concerning 

 the vascular system in Lachesis gramineus t, I pointed out that, 

 contrary to what is to be found in many Snakes, the intercostal 

 arteries perforate the body- wall accurately in the middle line and 

 singly. This feature, I am now inclined to believe, is distinctive 

 of the Viperidje, for I have since found a similar state of affairs 

 in Causus rhomheatus and Ancistrodon jnscivorus. 



Veins and Arteries of Lung. — Dr. Gadow, in a figure + of the 

 pulmonary arteries and vein of Crotalus, represents these vessels 

 as passing forward from the heart. This direction is of course in 

 conformity with the tracheal lung of that snake, where possibly 

 the respiratoiy organ lies entii'ely in front of the heart. In the 

 young Litis both ai-tery and vein bif ui'cate. The artery bifurcates 

 some little way after its origin, and the anterior branch supplies 

 the tracheal lung, while the posterior branch supplies that 

 portion of the lung which lies behind the heart. The pulmonary 

 vein shows the same general distribution. There were two main 

 branches, one anterior and one posterioi". The direction of 

 emergence from or of entry into the heart, as the case may be, was 

 rather lateral than definitely antei'ior oi- posterior. I deal on a 

 later page § with these facts with reference to the original form of 

 the lung in the Squamate reptiles. 



Veins of Neck (text-fig. 9, p. 38). — Contrary to what is to be found 

 in many Snakes, there are only two main veins of the neck in Bitis 



* P. Z. S. 1895, p. 705. t P. Z. S. 1904, vol. i. p. 366. 



X In Broun's Thierreich, Rept. Bel. vi. Abth. iii. Taf. cxxxvi. lijr. 2. 

 § Below, p. 41. 



