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Show bifurcate as in Python, &c., and thus supply both sides of the vertebral column. Interspersed among these are a few arteries which, as in Colubrines generally, plunge into the dorsal parietes on one side or the other of the middle line. There is in these arteries no question of a bifurcation. In this anterior section of the body from the junction of the two aortse I counted 16 bifurcated intercostals, and only three which were single arteries throughout supplying only one side of the body. It must be pointed out, however, that there is not here, as there is in Python, an artery to each intercostal space. There are interspaces of several vertebrae between consecutive arteries. Rarely there are arteries following each other immediately. For a considerable region of the body, beginning towards the end of the liver, the intercostals are mostly single trunks, and therefore entering the body-wall to the right or to the left of the dorsal median line as the case may be. Further back the arteries again become prevalently double. It is clear therefore that there are some grounds for comparing the intercostal arteries of this genus with the Pythons on the one hand and with the Colubrines on the other. The irregularity of those arteries in the Colubrines generally (though it must be remembered that after all our knowledge is at present very deficient) is shown in Erythrolampms, and coupled with this the bifurcation in the middle line before entering the body-wall of some of those arteries, which is a Pythonine characteristic. We may perhaps also see in this latter character a point of likeness to the Viperidae. In these Snakes there is up to the present no exception to the rule that the intercostal arteries arise irregularly, but enter the middle line of the dorsal parietes instead of to the right or to the left as in the Colubrines. The division of these vessels therefore takes place within the thickness of the parietes, instead of outside as in Python and its allies. It seems therefore that, starting from the conditions observable in the Boidse-and there is now much evidence for the reasonableness of the assumption that this family lies nearest to the base of the Ophidian series-we can trace the modifications of the intercostal arteries in at any rate two directions. The usual Colubrine arrangement may be derived, as I have already suggested *, by an obliteration, now on one side and now on the other, of one of each of the paired intercostals, the usual gaps being already indicated among the Boids by the secondary longitudinal intercostal trunks which are connected only at intervals with the aorta. The second path of development is completed in the Vipers, where in one way the Boid arrangement may be looked upon as more obviously preserved. It appears to me that Erythrolampms may be looked upon as a stage in this metamorphosis. The Boid character has been largely retained and the Colubrine character correspondingly feebly developed. The disappearance of the latter and a slight change (already referred to) in the former would give the Yiperine character. It is note- * P. Z. S. 1904, vol. ii. p. 108. 5 0 0 MR. F. E. BEDDARD ON THE VASCULAR AND [M a y 1 , |
