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Show 108 MR. F. E. BEDDARD ON THE [May 17, a primitive character. There is no a priori objection to deriving the Ophidia from some Lacertilian form in which the characteristic lacertilian " tag " to the heart was absent. In the genus Varanus, for example, the gubernaculum is absent, as others as well as I myself have observed ; and it may be pointed out that the Ophidia might well have been derived from some form in which, as in Varanus, the neck was long, the lungs firmly bound down to the dorsal parietes, the trachea or bronchi continued for a considerable distance through the lung, and the urinary bladder absent. The fact that in Eryx the right and left aortic arches are equal in size at their junction to form the unpaired dorsal aorta seems to me to be undoubtedly a primitive feature. I may furthermore observe that this feature is figured * by Dr. Gadow as characteristic of Pelophilus (Boa) madagascariensis. Apparently, however, Python bivittatus has unequal right and left aortee f . In other serpents it is common for the right aortic arch to be smaller than the left, and this is carried so far in Zamenis Jlagelli-formis as to give the impression that the right aorta is a mere inconspicuous forwardly running branch of the left J. § Intercostal Arteries. The intercostal arteries in Eryx jaculus show some interesting features, which are partly indicated in the accompanying drawing (text-fig. 19, p. 109). In the anterior region of the body the arteries in question arise from the left aorta immediately after it has parted company with the anterior vertebral. Anteriorly to this point some arise from the left aorta, but that region of the body is supplied from the vertebral artery. The intercostal arteries which arise from the right aorta and from the first part of the conjoined aortse are single trunks given off at irregular intervals not corresponding to the individual vertebra. They join above, however, to form a continuous and slender dorsal artery which may be termed the posterior vertebral artery (P.v.); from this arise at regular intervals the paired intercostals. After the end of this vertebral artery the aorta continues to give off the dorsal intercostals which, when they reach the median dorsal line, run along it for a short distance anteriorly and posteriorly, giving off as before paired branches to the intervertebral regions. But there is no formation here of a continuous longitudinal trunk running over more than three or four vertebra. So far the arrangement is precisely such as I have lately described in another Boid, viz. Python spilotes §. But whereas in the last * Broun' s Klassen und Orduungen des Thier-lieichs, Bd. vi. Abtli. iii. nl. cxxxv. fig. I-f Loc. cit. pi. xxxiv. fig. 2. The figure is copied from Fritscli. j Beddard, " Contributions to our Knowledge of the Vascular System in the Ophidia," P. Z. S. 1904, vol. i. p. 338. § " Contributions to our Knowledge of the Circulatory System in the Ophidia." P. Z. S. 1904. vol. i. p. 3tj2. |