The Heart of the Sea-Turtle. 333 



Prolonged stimulation of the vagus has notled,intheland 

 tortoise, to such pi-onounced results, as regards cardiac 

 inhibition, in the few cases examined by me, as in other 

 Chelonians. 



The Chelonians constitute morphologically a very compact 

 group, and it will be seen that the resemblances in the 

 physiological behavior of this group is in accord with their 

 anatomical likeness. It has been pointed out several times, 

 that C. Mydas is physiologically more closely related to the 

 Terrapin than the other species of sea- turtles I have studied ; 

 and it is in this one that the most anatomical resemblance, 

 as far as the cardiac nerves are concerned, is found. 



Throughout this paper, differences in the physiological be- 

 haviour of different species and genera of Chelonians have 

 been pointed out; but it must be remarked that many minor 

 variations, readily discernible by the eye, but not easily 

 expressed in words, have been noticed during the year over 

 which these investigations have extended. 



The explanation of the different action of drugs on animals 

 closely related anatomically, may possibly be reached by 

 some such comparison as I have endeavored to carry out for 

 the Chelonians. 



EXPLANATION OF PLATE. 



Fig. I. Eelations of the sympathetic, vagus, &c, in Chelonia im- 

 bricata and C. caretta. S., sympathetic ; V., vagus ; g.c.s., ganglion 

 cerv. super.; a. car., arteria carotida; g. v., ganglion of the vagus 

 stem ; g. c. m., ganglion cerv. med. ; g. c. b., ganglion cardiac, basal, ; 

 ace. s., accelerating symp. branch . a. v., arteria vertebralis : ix, x. 

 refer to the metamere concerned. 



Fig. 2. The vagus ganglion with its leash of branches, a. s., art. 

 subclavia. 



Fig. 3. Shows partial fusion of g.c.%., the gang. cerv. infer., and 

 g.tp., the gang, thoracic, prim. 



Fig. 4. The sympathetic, &c, in the Terrapin : to a large extent 

 the same in Chelonia mydas. The lettering, as in previous figures. 

 The dotted line between g.c.i. and g.c.b. indicates that a branch, 

 sometimes present, completes an annulus Vieussenii. 



Fig. 5. Ventricle with areas marked off by dotted lines, the 

 numbers indicating the order in which, these areas die- 



