ID A N A TO M Y A \ D P II Y S I L OG Y F 



s rpentina as our typical turtle, and will describe in detail the apparatus of 

 respiration as we rind it in this species, noting, subsequently, the modifications of 

 structure existing in the different genera that we have had the opportunity to 

 examine. In all turtles we nave found the .general plan of the respiratory apparatus 

 constant, an inspiratory muscle in each flank, and an expiratory muscle with four 

 bellies, two anterior and two posterior, connected by a broad membranous tendon, 

 inclosing the viscera and capable of compressing them against the under surface 

 of the dorsal shield. The discrepancies characterizing different genera principally 

 affect the origin of the anterior belly of the expiratory muscle; these may naturally 

 he arranged in two groups, those in which the origin is anterior (about the second 

 rib), (see Fig. 5) and extends nearly across the width of the shield, and those in 

 which the origin is posterior (about the third or fon'rth rib), and in extent more 

 limited. The specimens we have had the opportunity to examine are too few to 

 enable us to determine whether this structural diversity can be received as an element 

 in determining generic rank. We will content ourselves, therefore, at present, with 

 the description of each specimen, including a brief notice of its habits and shell- 

 measurements, which may serve as a nucleus for future and more extended 

 observations. 



Chelydra Serpentina is a carnivorous turtle living in the water, under bank-eaves, 

 or at the bottom of streams, and yet capable of moving over the land with facility. 

 The under surface of the body is much exposed, the plastron being small and 

 cruciform, and connected with the carapace by a narrow bridge, which widens to 

 join the fourth, fifth, and sixth ribs. The flank spaces are large, flat, and unpro- 

 tected, and the extremities incapable of complete retraction under the shell. The 

 height of the trunk compared with the width and length of the carapace is as one 

 to three and three and a half. 



Carefully watching the animal while breathing, we notice synchronous move- 

 ments of tin- trunk, of the throat, and of the glottis within the mouth. With the 

 first element of the respiratory act, expiration, the glottis opens, the hyoid apparatus 

 descends and widens, the shoulders sink and the Hanks become increasingly con- 

 cave; then follows immediately the inspiratory effort, the glottis remaining open, 

 the throat narrows, the flanks become tense, and the shonldcrs arc pushed forwards 

 as tin- act culminates; afterwards the muscles relax, the glottis closes, and the 

 creature is at rest until again impelled to renew the air in its lungs, when the same 

 sequence of expiration, inspiration and pause is repeated. 



We shall follow the order of the elements of the respiratory act in describing tin- 

 apparatus by which it is effected. And first, of the muscles of expiration. For 

 the purpose of dissection, it is desirable to place the animal upon its back and fix 

 it, by extending and securing its head, tail, and extremities. Separate with a saw 

 the bony bridges connecting the plastron with the carapace, and sweeping a knife 

 close to the inner surface of the former, divide from before, backwards, the deltoid, 

 pectoral, pelvic and flank muscles, the acromial articulations posterior to the first 

 pair of sternal bones, and the loose cellular bands binding the visceral sac to the 

 middle line. This permits the removal of the plastron. Drawing the shonldcrs for- 

 ward, cut the ligaments, holding the scapulae to the spine anterior to the first rib, 



