218 



COMPARATIVE PHYSIOLOGY. 



peculiar to it as it gradually approaches quiescence and death 

 — a matter of the utmost importance. 



If the student will then compare what he has learned of the 

 mammalian heart in this way with the hehavior of the heart 

 of a frog, snake, fish, turtle, or other animal that may be killed 

 after brief ether narcosis, without cessation of the heart's ac- 

 tion, he will have a broader basis for his cardiac physiology 

 than is usual ; and we think we may promise the medical stu- 

 dent, who will in this and other ways that may occur to him 

 supplement the usual work on the human cadaver, a pleasure 

 and profit in the study of heart-disease which come in no 

 other way. 



With the view of assisting the observation of the student 

 as regards the. heart of the mammal, we would call special atten 

 tion to the following points among others : Its method of sus- 

 pension, chiefly by its great vessels ; the strong fibrous frame- 

 work for the attachment of valves, vessels, and muscle-fibers ; 

 the great complexity of the arrangement of the latter; the 

 various lengths, mode of attachment, and the strength of the 



FJl 



Fie. 188.— Orifices of the heart oeen from above, after the anriclee and great vessels 

 had been cut away (after Huxley). PA , pulmonary artery with its semilunar valves. 

 Ao, aorta m a similar condition. It A T, right auriculo-ventricnlar orifice, with 

 7«. V. 1 and 2 flaps of mitral valve; b, style passed into coronary vein. On the loft 



Eart of LAYt^e section of the auricle is carried through the auricular appendage, 

 ence the toothed appearance due to the portions in relief cut across. 



inelastic chordae tendinese; the papillary muscles, which doubt- 

 less act at the moment the valves flap back, thus preventing 



