620 ME. F. E. BEDDARD ON THE [^'^'^y 29, 



on the right side, in common with the internal mammaiy '■'", from 

 which it soon diverges and runs the usual course to near the 

 dorsal middle line. 



It is remarkable that on the left side (only, not on the right) 

 the azygos arises by two origins — a thicker anterior trunk, and 

 a much more slender posterior vessel. This is quite analogous 

 to what has already been described in Crocodilus cataphractzis, 

 including the asymmetry, which is still more remarkable. The 

 azygos also gives off, precisely as in Crocodilus catcq^hr actus, a 

 vein running along the lateral thoracic parietes. Arrived at the 

 side of the vertebi-al coloumn some little vfay in front of the origin 

 of the longus colli muscle (also as in GrocodAlus catcqyhr actus), the 

 azygos does not plunge into the thickness of the parietes as in 

 the last-mentioned Crocodile, but runs back quite superficially as 

 in a Mammal. It is thus displayed for the whole of its course to 

 as far back as where the dorsal parieto-hepatic trunks communicate 

 with it. This course corresponded (at any rate in one of the two 

 specimens dissected) to 6 ribs. The chief difi'erence, therefore, 

 which this species shows from Crocodilus ccdaiilir actus is in the 

 possession of superficially running azygos veins. 



In Caiman sclerops the two azygos veins arise symmetrically 

 with regard to each other from their respective jugulars, light and 

 left. In both cases they arise behind and not very near to the 

 subclavians and separately from the jugular, i. e. not in common 

 with any other vein. Each is closely accompanied by the corre- 

 sponding artery which is a branch of the carotid. I could detect 

 no lateral parietal branch of each vein ; but as the specimen was 

 quite a small one, they may have remained undetected. Each 

 azygos reaches the dorsal line far forwards at the level of the 

 fourth rib in front of that whose veitebra bears the origin of the 

 longus colli muscle. Then the vein disappears and does not run 

 superficially on each side of the body ; but some way in front of 

 the liver it reappears and passes in a slightly sinuous course to 

 the end of the liver, where it gives rise in the usual way to the 

 hepatic branches, which will be described later. Thus the present 

 genus agrees to some extent with Osteolcemus in the superficial 

 course of the two azygos or posterior vertebral veins, there being 

 the difierence that in Caiman the vein runs superficially only 

 posteriorly. The artery is superficial throughout. 



Anterior Abdominal Veins. — These veins, which, as is well 

 known, are completely double in the Crocodilia, show certain 

 diflferences in different species. Rathke has called attention t to 

 the fact that the two veins often diff'er in calibre. He does not 

 mention certain points to which I shall now refer. 



In CroGodihis catajihracttis, as in Crocodilus acutus, a slender 

 vessel leaves the left anterior abdominal vein some way behind 

 the liver, and running obliquely forwards joins the right anterior 



* Whether this is also the case with G. cataphractus I am not able to say. 

 According to Rathke thej' are separate in origin, 

 •j- Loc. cit. p. 257 footnote. 



