370 ON THE CIRCULATORY SYSTEM IN THE OPHIDIA, [Feb. 16, 



From a classificatory point of view the main j-esult which I 

 have arrived at is the recording of certain facts which support 

 the general contention that the Boidse occupy a basal position 

 among the Ophidia. This view has of course been partly based 

 upon the persistence of rudiments of the hind limbs and of the 

 paired subequal lungs. The fact that the two aortic arches are 

 equisized is another fact pointing in the same dii'ection, as is also 

 the regular series (one to each intei'orbital region) of intercostal 

 arteries*. The dorsal body- wall, moreover, where these arteries 

 enter is more muscular and less tendinous in structure than in 

 many Snakes. It may, I think, fairly be held that the replace- 

 ment of muscle by tendon is secondary. In possessing a fairly 

 long azygous vein joining the vertebral vein on a level with the 

 anterior margin of the heart, Python spilotes differs from such 

 a form as Coronella getula, where the azygos is much reduced. 

 The latter condition seems to me to be in all probability the 

 derived one. The small number of arteries to the stomach, though 

 met with in other Snakes, is at any rate not at variance with the 

 views here advanced ; and I am of opinion that the single renal 

 artery on either side — the absence, in fact, of reduplication so 

 common in the Ophidia — is decidedly a primitive character. 

 Gadow, however, found two such arteries in the Madagascar Boa, 

 Felophilus madagascariensis t. 



I am unwilling at present to attempt any diagnosis of other 

 genera, though there are plain indications of the possibility of 

 utilising the arterial system for systematic purposes. 



* The further connection between these by superficial trunks is possibly to be 

 regarded as a secondary modification. 



•f See Bronn's ' Thier-Keich,' loe. cit. pi. cxxxv. fig. 1. 



