On the Anatomy o/'Eryx and other Boidse. 233 



keeled. Areola slightly wider than long, rounded at the 

 base, the apex bulging inwardly ; the base of posterior 

 median area smooth, the rest transversely striated ; the outer 

 apical areas are more strongly and widely striated. The 

 upper half of propleurse closely punctured, as are also the 

 mesopleurse ; the metapleurse are more closely and strongly 

 punctured. First segment of abdomen aciculated, the post- 

 petiole more strongly and raised in the middle ; the second 

 and third segments are closely punctured; the gastrocoeli 

 wide, striated, the oblicpue apex aciculated. 



XXIV. — Preliminary Note on certain Points in the Anatomy 

 of Eryx and other Boida?, partly indicative of their Basal 

 Position among the Ophidia. By FRANK E. BEDDARD, 

 M.A., F.R.S. 



It is generally believed that the Boidre occupy phylo- 

 genetically a place at or near the base of the Ophidian series ; 

 and this view is expressed by Boulenger in a tabular state- 

 ment of the mutual affinities of the various families of the 

 Order *. This opinion is largely based upon the persistence 

 of considerable vestiges of the pelvic girdle and upon the 

 paired lungs. In studying the anatomy of snakes I have 

 been able to note a few other points to which little or, in 

 some cases, no attention has been paid and which tend to 

 the support of this conclusion. My observations bearing 

 upon this subject were made upon Python, Eryx, and Boa. 



The first point to which I would draw attention is the 

 equal size of the right and left aortic arches, which join to 

 form the dorsal aorta. In at least many other snakes (for 

 example, Zamenis fagelliformis) the right aortic arch is so 

 much the smaller that it appears almost as an inconspicuous 

 branch of the left. It would appear, however, that in Python 

 hivittatus this is not the case f, though Dr. Gadow's drawing J 

 of Pelophilns madagascariensis is in accordance with the facts 

 which I have observed. 



Secondly, the intercostal branches of the aorta are arranged 

 in a fashion which appears to me to be distinctly archaic. 

 In most snakes the intercostal arteries are very irregular in 



* ' Catalogue of the Snakes in the British Museum (Natural History), ' 

 London, 181)3, vol. i. p. 2. 



f Bronn'a ' Klassen und Ordnungen dea Thierreiclis,' Bd. vi. Abth. iii. 

 pi. exxxiv. fig. 2. This figure is copied from Fritsch. 



[ ibid. pi. exxxv. fig. 1. 



