1907.] AZYGOS VEINS IN MAMMALS. 185 



inferior. It does not, however, consist only of a region lying- 

 behind its point of entrance into the auricle ; but a branch also 

 runs forward supplying four intercostal spaces, the first being that 

 between ribs 2/3. The vein does not join the superior intercostal. 

 But it will be noted that rib interspace 2/3 has on the right two 

 veins. 



Ourehia nigricaudata is much like R]uq)hicerits . The vena cava 

 anterior receives a pair of veins, the superior intercostals, which 

 bring back blood from the region of the first rib only. The two 

 veins are not absolutely symmetrical as to their point of entrance 

 into the vena cava. The second to the fifth rib inclusive supply 

 four intercostals which unite to form the right azygos. On the 

 left side of the body the azygos consists of an_ anterior and a 

 posterior section which imite at their communication with the 

 right auricle. The anterior vein is very slender, excepting in the 

 region at and near to its fusion with the posterior vein. The 

 azygos proper, i. e. the posterior section, is a stout well-developed 

 vein which receives blood from the intercostals on both sides of 

 the body, It ends at the diaphragm in a bifurcation formed by 

 the two intercostals supplying the last (the thirteenth) ribs. 



Cephalophus grimmii showed an identity of arrangement in two 

 examples, one a male, the other a female. The better developed 

 left azygos entered the heart in company with the vena cava 

 inferior, and not by a separate orifice. On the right side of the 

 body the azygos consisted certainly of four intercostal affluents. 

 The last two of these (at any rate in the male example) encircled 

 the fourth rib. C. maxwelli shows much the same relation to 

 C. grimmii that the two species of Gnu show. For the left azygos 

 opens into the precaval. But it gives off a branch to the auricle. 

 Oryx leucoryx has also a comparatively short right azygos 

 composed, however, certainly of five intercostal branches. The 

 longer left azygos enters the heart either directly or with the 

 vena cava inferior. Above the influx of the right azygos is a 

 single inferior intercostal on the right side of the body, and on 

 the left side a corresponding vein which, however, immediately 

 divides into two trunks. There was, however, no connection 

 between the posterior of these two veins and the lower section 

 of the azygos system. 



The arrangement of these veins is much the same in Oryx heatrix 

 as it is in Oryx leucoryx. The left and principal azygos commences 

 with the interspace between ribs 6 and 5. Above this is a vena 

 suprema intercostalis, composed of only two branches lying in the 

 first two rib interspaces. To this corresponds exactly on the right 

 side a vein which draws blood only from the first intercostal space. 

 Behind this the right azygos opens into the precaval opposite to 

 the second or third rib. Its branches extend back to the sixth 

 rib, and they begin w-ith the second intercostal space. 



i have selected for figuring here (text-fig. 62) the azygos and 

 immediately related veins of Cervicapra bohor, on account of their 

 splendid condition in the male example which I had the opportunity 



