Proceedings of the General Meetings for Scientific Business of the Zoological Society of London 1905 vol. 2

Page 80

1905 ] ANATOMY OF THE FERRET-BADGER. 29 arteries and afterwards divide into right and left halves. The first pair of intercostals corresponds to the first branch of the Azygos *. The first six pairs of intercostals lie entirely to the left of the Azygos; the 7th artery on the right side and those which follow lie to the right side of the Azygos. This point, I take it, is where originally the now missing right aortic arch joined the left aortic arch. In this region the aorta also gives off a number of fine slender branches to the oesophagus and to the lungs. The first of these branches arises a little way down the first right intercostal and supplies the windpipe; from or in the immediate neighbourhood of the next four right intercostals arise twigs for oesophagus and lungs; then follows a gap of two intercostals, the last twigs arising from the 8tli right intercostal. From the last intercostal in front of the diaphragm arises a diaphragmatic artery on each side ; another diaphragmatic artery springs directly from the aorta behind the diaphragm, and independently of an immediately following suprarenal artery. I have carefully and, I hope, exactly compared the pre-diapliragmatic arteries of Helictis with those of its ally Galictis and with those of the iEluroid Suricatci. The former, as might be expected, shows greater resemblances to Helictis than does the latter. There are, however, also differences. There are 10 instead of 11 pairs of intercostals in front of the diaphragm, or, to be more absolutely accurate, 10 on one side and 9 on the other; for the first intercostal has not a fellow and belongs to the left side. The fifth right intercostal is the first which passes to the outside of the Azygos vein. The pulmonary and oesophageal branches arise in every case from the right intercostal vessels, and I counted four of them which have the following position : the first three arise from the first three right intercostals; the fourth springs from the fifth right intercostal. In Suricata tetradactyla there are 12 intercostals on the right side in front of the diaphragm and two additional ones on the left side. The most important pulmonary and oesophageal arteries arise separately from the aorta, though some spring from right intercostals. The 8tli right intercostal is the first which passes over the Azygos vein. * This vessel, as in most mammals, is present only on the right side.