RESPIRATION IX THE CHELON1A. 17 



three-fourths of an inch, and the outer one; stretching along the intercostal space 

 and across the shield, one inch and three-eighths ; from this origin the fihres spread 

 over the anterior part of the lung and arc inserted into the common tendon and 

 into the peritoneal covering of its under surface. The posterior belly is similar to 

 that of P. rugosa, the muscular band underlying the bridge which joins the carapace 

 and plastron being somewhat wider. The dimensions are— length, 8| inches; 

 width, (! inches; elevation, 3j inches. 



In Malacoclemmys palustris, Ag., the inspiratory muscle is the same as in Geo- 

 graphica. The anterior belly of the expiratory muscle arises from the third and 

 fourth spaces at their vertebral margins, and from a line running across the shield 

 to the fourth rib, diverging at an angle of about 70°. 



The posterior belly is like that of geographica. The dimensions are — length, 7 

 inches; width, 42 inches; elevation, 3| inches. 



Chrysemys picta, Gray. — Inspiratory muscles as in E. terrapin. The anterior 

 belly of the expiratory muscle arises from the vertebral margins of the third and 

 fourth intercostal spaces and a slip from the fifth, and from across the carapace to 

 the junction of the fourth and fifth ribs, the divergence being about 30°. 



The posterior belly as in geographica. Dimensions— Length, 4| inches; width, 

 3| inches; elevation, 1| inches. 



Of the second and third subdivisions we have examined no specimens. The 

 fourth, Clemmydoida?, is characterized by "their more arched though elongated form, 

 and the more compact structure of their feet, the front and hind pairs of which 

 arc more nearly equal, and their toes united by a smaller web ; they are less 

 aquatic and generally smaller than the preceding." Of these we have dissected 

 representatives of three genera, Nancmys, Calemys and Glyptemys. 



In Nancmys guttata, Ag., the inspiratory muscle presents no peculiarities. The 

 anterior belly of the expiratory muscle arises from the vertebral margins of the 

 second and third intercostal spaces and from part of the fourth, and from the posterior 

 edge of the second rib as far as its extremity ; from this extensive origin the fibres 

 descend over the lungs, covering the front and anterior part of their lateral walls. 



The posterior belly resembles that of the Snapper. Dimensions are — length, 

 4^; inches; width, 2$ inches; elevation, l T 9 g inches. 



In Calemys Miihlenbergii, Ag., the muscles are the same as in guttata. Dimen- 

 sions — length, 3s inches; width, 2S inches; elevation, If inches. 



In Glyptemys insculpta, Ag., the muscles are the same as in guttata. Dimen- 

 sions — length, 4 r 3 g inches; width, 3 T 7 g inches; elevation, 1| inches. 



In the fifth subdivision, Cistudinina, "the body is remarkably short and high, 

 slightly oblong, and almost round. The plastron, which is movable upon itself 

 and upon the carapace, as in the Evemydoidre, is also connected with the carapace 

 by a narrow bridge ; but the feet are very different, the toes, as in the Tcstudinina, 

 being nearly free of web. Their habits are completely terrestrial." Of this sub- 

 family we have examined one species, Cistudo Yirginea, Ag. The flank spaces 

 in which the inspiratory muscles play are extremely deep, owing to the high 

 carapace. The amount of muscular fibre is relatively greater than in the other 

 turtles, and the central tendon is narrow, and irregularly triangular in shape. The 



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