AORTIC LIGAMENT IN INDIAN FISHES. 



73 



powerful construction to be at all effective. For the suspended 

 ligament to be of any use as a diagonal curtain, it is evident that 

 the aorta, as part of the body, will have to undergo flexion, 

 the curtain remaining taut and straight, but, curiously enough, 

 comparison of the statements in the tables (pp. 70-72) shows that 

 it is just in those fishes in which, owing to a deep thick body 

 and envelopment by deeply grooved vertebral and stout hsemal 

 arches, the aorta cannot experience much lateral flexion, that the 

 ligament exists. 



Text-figure 5. 



A diagrammatic representation of the position of the ligament inside 

 the aorta during the lateral flexions of the body. 



aor., aorta; ?/_9'., ligament. 



On the other hand, the aortic ligament is absent or but feebly 

 developed in all, or most of, those fishes in which the body is 

 slender, and the median (especially the median dorsal) fins 

 elongated in form, or the caudal region very much elongated 

 (narrow and tapering), i. e., in just those fishes in which flexion 

 of the body and therefore of the aorta must be most marked. 



This correlation of facts, founded on my examination of over 

 80 species of fishes, certainly does not appear to favour the 

 hypothesis as to the mode of action of the aortic ligament 

 suggested by Professor Stewart. 



Since I have no theory of my own to offer concerning the 

 raison d'etre of the aortic ligament, I will merely add that it is 



