1907.] AZYGOS VEINS IN MAMMALS. 195 



The corresponding ribs on the right side Avere supplied with 

 veins joining the long right azygos. The azygos system of Hyrax 

 has been partly described by Brandt* in a memoir upon the 

 general anatomy of Ilyrax, who observes that the vena cava 

 posterior enters the right auricle " nachdem sie die vorderen 

 Vence intercostales und die Vena azygos aufgenommen." The same 

 fact, according to Weber t, has been also noted by George % ; but 

 I have not had the opportunity of studying this paper §. Nothing 

 is said by Brandt concerning the right azygos. It is, I presume, 

 legitimate to compare the descending region of the left azygos in 

 Hyrax with the left anterior cava. In a second specimen I did 

 not find a left azygos oj)ening into the vena cava inferior. But 

 I am. not inclined to deny its existence. The large right azygos 

 was equally well developed in this example. 



In a third example of Hyrax caj^ensis (a female) the azygos 

 system was entirely develojaed upon the right side of the body, 

 and differed considerably from that of the two individuals just 

 described. The main azygos stem (text-fig. 66) was traceable 

 to the lumbar region, where it communicated with the vena cava 

 inferior (not opposite to the renal vein) in common with a lumbar 

 vein. The vein undoubtedly belongs to the right side since it 

 lies on the trachea on the right side of that tube. Its mode of 

 termination anteriorly is, so far as my own experience goes, unusual 

 among mammals. Instead of entering the jugular some little 

 distance in front of the heart, as is elsewhere (so far as I have seen 

 in my own dissections) invariably the case with the right azygos 

 when present, it enters that vein so near to its entry into the 

 auricle that it may almost be said to enter the auricle separately ||. 

 But there is, of course, no question as to a direct communication 

 with the coronary sinus, like the left azygos of the Cavicornia. In 

 front of this vein, which debouches into the heart opposite to the 

 fifth rib, is a small vein which receives blood from the 2nd and 

 3rd intei'costal spaces. 



The disposition of the azygos veins in the Artiodactyle Ungu- 

 lates seems, therefore, to be fairly constant in the group, though 

 the left azygos does not quite invariably open directly into the 

 right auricle oi' into the vena cava posterior just before the open- 

 ing of the latter into the right auricle. This arrangement of the 

 left azygos has not been found in any other group of mammals 

 excepting only in the Mole, where it has been stated to be the 

 same as in the Artiodactyles. Possibly this fact may be con- 

 sidered as requiring confirmation. It is, however, interesting to 

 note that as an abnormality the left azygos in man may open 

 into the right auricle directly. I have not attempted to compare 



* Mem. Ac. St. Petersbourg, ser. 7, t. xiv. p. 65. 



f Die Sangetieve, Jena, 1904. 



X Bibl. Ecole Hautes-Etudes, Sec. So. Nat. xii. 1875. 



§ In an earlier paper bj' George (Ann. Sci. Nat. (6) i. 1874) a right azygos onlj' is 

 described. 



II This is also the case with the Horse, according to Chauvean and Arloing. I have 

 also described the same arrangement in Tragulus. 



13* 



