1910.] ANATOMY OF HIPPOPOTAMUS AMPHIBIUS. 231 



it, the mouths of origin of lung arteries. After a short gap 

 there is a group of four arteries placed as is shown in the figure 

 and crowded very close together. So close indeed, that the 

 appearance of one artery with a cribriform plate at its aortic 

 aperture is produced. Of the four, one or two are also lung 

 arteries, as I ascertained by means of an inserted seeker. The 

 others are intercostals. Then follow two arteries, one behind the 

 other, which are placed rather more closely in sequence than 

 those which follow. The latter form a series which are wider 

 apart and perfectly regular until the end of the series, which, as 

 already mentioned, is not shown in the drawing. It is to be 

 noted, therefore, that the intercostals of this animal are quite 

 unpaired at their origin from the aorta ; the division occurs, 

 however, shortly after the origin. The most important point of 

 difference from the intercostal series of such other Mammals as 

 I have had the opportunity of seeing, is in the mass of four 

 arteries situated so close together at the beginning of the series, 

 and which are lettered in the accompanying text-figure. The 

 unpaired condition of the intercostals is perhaps rather less 

 common among Mammals than a paired origin of these arteries. 

 It is furthermore to be noted that there were no visible oesopha- 

 geal arteries on the opposite side of the aorta in this region of 

 that arterial trunk. Such arteries are commonly ventral instead 

 of dorsal in position, and thus contrast with the intercostals and 

 lung-arteries, which must be regarded as being one morphological 

 series. It may be, however, that in the Hippopotamus the 

 oesophageal arteries are derived from twigs of the intercostals ; 

 but as to this I have no positive information to offer. 



The azygos vein is mentioned by Gratiolet only in the observa- 

 tion that " Les libres communications de l'azygos et des veines 

 mammaires avec la veine cave superieure indiquent que les 

 muscles locomoteurs du tronc sont, ainsi que les centres nerveux, 

 soustraits a toute case de congestion." In examining the thorax 

 of the recently dead animal the apparent inconspicuousness of the 

 azygos was striking. This was possibly due to the pleura of the 

 thoracic wall being rather thick, but in other large animals such 

 as the Zebra, where I have observed the azygos, it was perfectly 

 obvious without further dissection, and I have figured it without 

 difficulty in a number of Antelopes. So difficult to detect is this 

 vein in Hippopotamus, that I had noted, before proceeding to 

 dissection of the neighbouring parts, that the vein was absent as 

 a distinct vein. I had in fact expected to meet with the condi- 

 tions that appear to characterise the Oetacea, a state of affairs 

 that would not perhaps have been unexpected. Nevertheless it 

 does not occur, as 1 ascertained after the heart and lungs were 

 removed, and therefore too late to give all the details desirable 

 about this important vein in a type where it is likely to be 

 interesting. I did, however, ascertain certain facts which are of 

 importance in the systematic placing of this Ungulate. In the 

 first place, there is a long azygos vein on the right side at any rate. 



