1907.] AZYGOS VEINS IX MAMMALS. 221 



of a more primitive position of the Ductus Cuvieri in animals 

 which possess as a rule two azygos veins, and are thus also 

 primitive in this peculiarity, and which moreover are usually 

 assigned on these grounds to a low place in the Mammalian 

 series. The whole grovip of facts fit in with each other in pei'fect 

 harmony. J believe that these facts are not without importance 

 in considering the Artiodactyle Ungulates, or rather the hollow- 

 horned Ruminants and the Pig tribe, which agree in the characters 

 of the azygos veins. 



The right azygos in these animals is always situated far forwards, 

 beginning even (e. g. in Oryx heatrix) with the second intercostal 

 space, and although the left and prevalent azygos does not occupy 

 what is ex hyj)othesi a primitive position, there are nevei^theless 

 true azygos veins present. The antei-ior section of the azygos, 

 which runs forward of the point of opening into the heart, is 

 perhaps to be regarded as the left precaval otherwise missing. 

 There is thus some agreement with the suggestions already 

 made. 



(12) The Venoi Tntercostcdes Siq^remce. 



These veins, so named by Hochstetter, and often termed inferioi 

 intercostals, are superficial veins made up of one or moi-e of the 

 intercostals anterior to those which unite to form the azygos 

 vein or veins. They are the superficial superior intercostal veins 

 of McClure*. As will be gathered from the foregoing pages, these 

 veins are not invariably present as trunks opening into the vena 

 cava superior ; nor indeed are they invariably present at all. I 

 presume that in these cases, whei-e no such veins are apparent, 

 the circulation is effected by the deep series of intercostal veins 

 lately figured t with gi-eat elaboration in the Opposum by Dr. 

 McOlure in the paper already referi-ed to. The details of the 

 occurrence of these veins in various genei-a of mammals have been 

 already dealt with in the foregoing pages. From these it will 

 appear that the veins in question are by no means of univei'sal 

 occuri'ence, and that when they do occur they are not always 

 connected with the precaval vein or veins. In man, for instance, 

 these veins are described as entering the left and right vente 

 anonymse respectively. This appears to hold good for the Primates 

 generally. 



But I do not profess in the present communication to have dealt 

 at any length with the Primates. Among the Oarnivora these 

 veins are evidently not common, and when they do occur some- 

 times join the precava and sometimes the vena or vense anonympe. 

 In the Marsupials also the venfe intercostales suprem8e are not 

 universal, but when they are met with they seem as a rule to 

 join the precaval or precavals. These veins are much more 

 general among the Hystriciform Rodents, where indeed, so far 

 as my observations go, they are practically universal and join the 

 precaval. As a rule, too, in this gi^oup the veins are paired and 



* Amer. Jonrn. Anah vol. ii. 1903, p. 371. f Loc. cit. fig. p. 380. 



