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Show 370 OX THE CIRCULATORY SYSTEM IX THE OPHIDIA. [Feb. 16, From a classificatory point of view the main result which I have arrived at is the recording of certain facts which support the general contention that the Boidae 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 direction, as is also the regular series (one to each interorbital 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 replacement 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, Pelophilus 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 hetvveen these hy superficial trunks is possibly to be regarded as a secondary modification. f See Bronn's ' Thier-Keich,' loc. cit. pi. cxxxv. fig. 1. |
