1906.] VASCULAR SYSTEM OF THE CROCODILIA. 619 



kinds of Crocodiles. This vein (the vena vertebralis communis) *", 

 is stated to arise from the anterior cava as a single trunk and to 

 have a very short course superficially along the vertebral column, 

 disappearing from sight — "nach dem er die vierte V. intercostalis 

 absesendet hat in den Kanal des Riickgrats um sich mit den Yense 

 spinales zu verbinden." It has thus, as he remarks, only a short 

 course, which terminates immediately behind the fourth rib. 

 There is no indication given as to what species or which species 

 this description refers to. The general account of the venous 

 system is stated merely to refer to " altere Krokodilen," though 

 definite species are now and again referred to in footnotes appended 

 to the description; not so, however, in the case of the veins which 

 concern us here. There is no evidence that I can extract which 

 points to any particular species. I find, however, that there are 

 variations, and that the three species which I have examined do 

 not agree. 



In GroGodilus cataphr actus the azygos veins answer pretty well 

 to the descriptions given by Rathke ; though there are certain 

 differences, and also some other matters not touched uj)on by 

 Rathke, to Avhich I desire to direct attention. The number of 

 ribs in this species is not mentioned by him f. I find that there 

 are only 12 pairs, i.e. 2 false anterior ribs, 7 true ribs, 3 posterior 

 false ribs. The azygos veins are of exactly the same size on both 

 sides of the body. They arise from the anteiior cava on each 

 side behind the origin of the subclavian. On the right side of 

 the body the origin was by two distinct affluents, forming with 

 each other and the vena cava a triangle +. I did not find any 

 such double origin on the left side. The vein runs in a direct^ 

 transverse direction (^. e. transvei-se to the longitudinal axis of the 

 body), and close to the vertebral column on each side plunges at 

 once into the parietes. Thence it never reappears upon the 

 surface of the musculature as a longitudinally running vessel, but 

 remains completely buried and hidden below it. 



The azygos vein is closely accompanied by the corresponding 

 artery (arteria vertebralis communis), which also rises below the 

 sui'face of the musculature, but is visible at intervals below the 

 peritoneal membrane. At a point about halfway between the 

 origin from the vena cava and the disappearance into the parietes, 

 both artery and vein give off a longitudinally and posteriorly 

 running branch along the lateral body- wall which has its counter- 

 part (in the case of the vein) in Varanus §. 



In Osteolcemtts tetraspis the azygos veins show features of differ- 

 ence which obviously aid in establishing the justice of the generic 

 separation of this Crocodile. As the following statement of fact 

 is based upon the examina,tion of two individuals, I imagine that 

 it can be taken as a description of the normal conditions obtaining 

 in this species. The azygos arises from the vena cava, at least 



* Zioc. cit. p. 255. f JLoc. cii. p. 55. 



X Cf. p. 620, where the same state of affairs is described in Osteolcemus tet7-asvis. 



^ See p. 616. 



