702 ON THE STRUCTURE OF THE LESSER ANTEATER. [June 15, 



to the first mentioned and not more than one third of its calibre, 

 which was also distended with blood. I believe that so marked a 

 difference in size between the two postcaval veins, when there are 

 two, is not an even exceptional occurrence among Mammals. It 

 recalls the unequal postcavals in the Lacertilian genus Tiliqua. 

 In Lizards the two postcavals are apt to be equal, but among the 

 Skinks are at least sonietimes unequal in calibre. There is no 

 question, it will be noted, in Orycterofus of a minute dis- 

 agreement in size between the two postcavals. The difference is 

 so great that the left-hand vein was in the first place altogether 

 overlooked and regarded as being merely the proximal end of the 

 spermatic vein of that side of the body. It is thus important to 

 recognise a well-marked difference between Orycteropus and other 

 Edentates at the very first. Still there remains the more 

 important fact of the double nature of the postrenal section of 

 the postcaval. The less important part played by the left-hand 

 division in the venous system of this Edentate as compared with 

 other Edentata is also shown by the posterior ending of the 

 left postcaval and by the origin of the intercostal veins. As to 

 the former point, it is to be noted that the large right-hand post- 

 caval, arrived at the posterior end of the abdominal cavity, divides, 

 as usual in animals with but a single postcaval vein, into the 

 two iliacs. These in the usual Avay undei-lie the aorta and its 

 postei'ior bifurcation, as is shown in the accomjDanying illustration 

 (text-fig. 225, p. 701). When the left-hand postcava is followed 

 backwards it is seen to open into the left iliac vein. Of this vein 

 it is clearly a rather unimportant affluent, for the main trunk 

 i-eaches the right postcava. 



The arrangement of the two postcavpe is thus different from 

 that of other Edentates, where the independence of the two 

 trunks is emphasized by the fact that each is concerned with the 

 iliac vein of its own side, or if there be a communication between 

 them it is of such a kind as not to interfere with the eqvial 

 importance of the two veins, such as, for example, the two 

 communications which I have figured in the Inseetivore Centetes 

 ecaudatiis *. The remaining point of diflerence between the two 

 postcaval veins concerns, as has been stated, the intei'costal veins. 

 Of these there are three lying between the point of bifurcation of 

 the veins and the right-hand spermatic vein. The intercostal 

 veins however, have nothing whatever to do with the left post- 

 caval trunk. They all open into the large right postcaval 

 and rather to the left of the vessel so that their position is very 

 nearly, if not actually, median. They were of small size although 

 they were full of blood, and the first of the three divided 

 immediately after, or rather before, its entrance into the right 

 postcaval into two branches, an anterior and a posterior. The 

 veins, in fact, are not paired as right and left trunks. 



There is thus in Orycteropus an approach to the more usual 



* P. Z. S. 1909, p. 511, text-fig. 136, A. 



