1909.] STRUCTURE OF THE LESSER ANTEATER. 697 



with perfect regularity, a branch on the posterior side of each 

 rib. There are eleven such branches behind the point where the 

 azygos in front opens into the anterior caval to form the ductus 

 Cuvieri. To each of these also of course corresponds an inter- 

 costal artery. Throughout the whole of its course the intercostal 

 arteries underlie the azygos when viewed in the ordinary position 

 of dissection. That is to say, they are dorsal to it. The azygos 

 ends, after the last branch already mentioned, without any 

 diminution of calibre by plunging into the thickness of the body- • 

 wall. It is only after this point that the intercostal ai^teries 

 are visible throughout their whole extent from their origin from 

 the aorta to their entering the body-wall. This state of affairs 

 conti'asts with that of, at any I'ate, a large number of mammals 

 including, as already mentioned, Chiromys. In all mammals 

 which I have hitherto examined as to this point, the first set of 

 intercostals, varying in number in different mammals, underlie 

 the azygos, and then at a fixed point, varying for the species or 

 genus, they cross over the vein overlying it in the position in 

 which they are seen on dissection. So that the intercostal 

 arteries can be divided into two series, of which one set are 

 dorsal and the other ventral to the azygos. This difference in 

 the conditions found among mammals has no relation, as it 

 would appear, to the length of the azygos. They sometimes 

 cross the azygos some way from its end in cases where the vein 

 extends quite as far back towards the diaphragm as it does in 

 Tamandua tetradactyla. Posteriorly the aorta divides into two 

 branches, each of which at once divides again to form external 

 and internal iliacs. The caudal artery arises from the right-hand 

 inner iliac. 



Postcaval veins and their branches. — In a recent paper upon 

 the postcaval vein in Mammals I have, I believe, quoted the 

 authorities for the principal facts known about the main venous 

 trunks of the Edentata. I need not, therefore, recapitulate the 

 literature here. It is not, however, certainly known Avhether 

 Tamandua agrees with other Edentates in the double postrenal 

 section of the postcaval. It might well be inferred, however, 

 that this was the case on account of its close resemblance in other 

 characters to Myrmecojjhuga. As a matter of fact Tamandua 

 tetradactyla has double postrenal jDOstcavals, which I am now able 

 to describe together with their principal branches. The postcaval 

 vein is double from quite the beginning of the kidney region, as 

 is also the case with Myrmecophaga. The renal veins, which are 

 single, are given off from the divided part of the postcaval, in 

 both of which particulars this Edentate differs from some others, 

 for example from Tattisia peha *. The divided postcaval, after the 

 origin of the renals, closely embraces the aorta which just fills up 

 the gap. 



The spermatic veins, as in other Edentates, arise from the 



* Beddard, " On the Postcaval Vein," P. Z. S. 1909, p. 509, text-fig. 135. 



