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Show 1 9 0 5 .] VASCULAR SYSTEM OF LACERTILIA. 487 bcena are not joined by ductus Botalli to the systemic arch. The left systemic arch in A. brasiliana is considerably larger than the right. The left anterior vertebral artery is not exposed for the whole of its course within the body-cavity. Shortly after its origin from the right aortic arch, and while its course is still oblique and towards the left side of the body, it is covered by a muscular layer, which is a continuation of the thick muscle covering the vertebral centra in the cervical region, and forming a soft cushion for the oesophagus to rest upon, and corresponding, I presume, to the longus colli. This muscle (see text-fig. 69, p. 486), after crossing the left anterior vertebral artery as already mentioned, becomes more and more slender and disappears. It is important to note that it is not symmetrical, and that no corresponding slip covers the right anterior vertebral artery. This curvature of one artery at least by a muscular slip seems to me to have a bearing upon the homology of the arteries. The origin of these arteries from the right aortic arch, and the fact that one springs from the aortic stem in front of the other, is a distinct point of likeness to the subclavians of other Lizards, which give off an anteriorly running vertebral. The loss of the fore limbs and the increased importance of the neck for burrowing purposes might account for the disappearance of the main subclavian stem and the increase of its vertebral branch. The burrowing of the artery in question beneath the musculature to which I have referred is found in the case of the subclavian of Tiliqua*. There are three very slender oesophageal arteries arising from the aorta. They are followed by three gastric arteries, of which the last lies a little way behind the gall-bladder. The mesenteric arteries have been shown by Rati ike f to differ considerably among the Amphisbaenidae. In the species examined by me there is a coeliac artery followed by a common mesenteric ; the intestine is also supplied by a posterior mesenteric which arises from the aorta among the renal arteries. The spermatic arteries arise just after the arteria mesenterica communis; the right is slightly in advance of the left. They both arise in common with an intercostal. On the left side an additional spermatic artery arises very close behind the main one. Behind the spermatic arteries a number of fine arteries supply the vas deferens. Of these I counted six on the left side, and there are about as many on the right. As a rule (five on the left side), these arteries arose directly from the aorta and independently of the intercostal arteries. The renal arteries differ in number on the two sides of the body. I counted four on the left and five on the right side. * Beddard, P. Z. S. 1904, i. p. 465. t Abh. Ak. Wiss. Miincheii, ix. (1863). See also Hochstetter, Morph. Jahrb. xxvi. (1898). P r o c . Z o o l . S o c .-1905, V o l . II. No. XXXIII. 33 |