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Show 1 9 0 6 .] RESPIRATORY SYSTEMS IN THE OPHIDIA. 5 1 3 more laterally. In Boa constrictor the same area is drawn from, but there is more specialisation in the veins. There are, in fact, two longitudinal trunks, one of which is lateral in position and the other close to the medial dorsal line. These arise by separate origins from the jugular. The branch of the azygos which draws blood from the immediate neighbourhood of the vertebral column does not form a long vessel running freely in the body-cavity. It divides directly after its opening near the heart into three equally sized branches, which run straight to the body-wall and plunge into the parietes between two successive vertebra?. This specialisation of the azygos into a proximal and a more distal trunk is an approach to the conditions observable in the Crocodilia, and is an advance upon the structure which has been as yet recorded among most of the Ophidia. In Python sebce, however, there is a similar division of the azygos into two branches concerned with different regions of the dorsal parietes*. A specimen of Python sebce which I have dissected since writing the account of the azygos of that snake referred to below affords confirmation of that account (which is of importance in view of getting at the normal arrangement of the veins in these animals) and enables me to add a few details. In the individual to which I now refer, a female, the azygos shows the same division into a more dorsal and a more lateral branch. The trunk is bifid behind the point where the third intercostal is given off from the undivided trunk. The more lateral branch only supplies three intercostal spaces. After this point the main trunk gives off eleven branches to as many rib-spaces, the last two of which are very slender. There is then a gap, but the very next rib is accompanied by a vein which is the first of a continuous series of fourteen intercostals arising from the right side of the median line which communicate with the hepatic portal system. So large a development of intercostal veins on the right side is not common in Snakes. On the left side, in this specimen as in other snakes, there is a strong development of the longitudinal parietal vessel. Remains of Umbilical Vein.-In the case of Boa cliviniloqua the male and female examples which I dissected showed traces of the umbilical vein (text-fig. 91, p. 514). I do not think that there were any noticeable differences in the several examples. But I made more complete notes in one case than in the other. In the larger female specimen the vena cava, immediately after emerging from the liver, was joined by a slender vein expanding somewhat at its debouchment into the vena cava. The extreme anterior end of the liver occupied the angle formed bv the confluence of the two veins. Traced backwards, this affluent of the vena cava continued to be full of blood for some little distance ; but soon it seemed to be impervious, and to be a mere ligamentous * See Beddard, " Contributions to the Anatomy of the Ophidia," P. Z. S. 1906, |