RESPIRATORY ACTIONS OF REPTILES. 531 



their respective bones in an inverted order: instead of their 

 moving the extremity, the extremity becomes the fixed point : 

 the bones answering to the clavicles are moved forward, and the 

 bones of the pelvis at the lower part are pushed against the inside 

 of the breast-bone, so that the whole bone is pushed out. They 

 appear to draw in their breath but once in twenty minutes or 

 half-an-hour, and often at a much longer interval.' 1 



It is probable that such respiratory actions could not be per- 

 formed by the animal when swimming and diving; and it is 

 certain that such actions of the limb-muscles could not effect 

 any motion of the breast-bone in the great proportion of the 

 Chelonian order, in which the plastron is fixed. The capacity 

 of the thoracic-abdominal cavity may be slightly affected by the 

 movements of the limbs acting on the soft walls at its fore and 

 and back parts, fig. 149, p. 233 ; the diaphragmatic muscles, 

 figs. 150, 151, 42, may cooperate; but respiration goes on when 

 the limbs are motionless, and apparently by acts of deglutition, as 

 indicated by the ' working of the throat.' 



In Ophidia, Lacerttlia, and Crocodilia, respiration is performed 

 by the expansion and contraction of the more movable parts of 

 the parietes of the cavity containing the lungs : for this being 

 dilated the air rushes in by the only available passage, viz. the 

 glottis and windpipe, to the lungs. The articulations of the ribs 

 in serpents allow of their rotation forward and backward, and 

 even of a slight divarication of the two ribs of each pair. This 

 mechanism and the muscles concerned in Avorkino; it are described, 

 pp. 55, 56, 224, figs. 143, 144. To whatever degree the visceral 

 cavity may be so expanded, the air enters by the nostrils or 

 glottis, if they be open and free; and a general expansile or 

 inspiratory movement may then be noticed. 2 But the great 

 length of the thoracic-abdominal cavity and the numbers of pairs 

 of moveable ribs — in some serpents three hundred pairs — are 

 associated with partial enlargements and contractions of the 

 cavity, effecting corresponding changes in the long pulmonary 

 bag, without affecting the total volume of air in it, if the glottis 

 be not in communication with the outward air, either directly or 

 through the medium of the nostrils. Schlegel has observed about 

 thirty such partial dilatations of the trunk and lung between two 

 inspirations. 3 When the Constrictors swallow their prey the 

 glottis is protruded from the mouth : this may be a consequence of 

 the pressure exercised on the parietes of the greatly distended 

 mouth, and may not relate to the necessity of directly receiving 



1 ccxxxvi. vol. ii. p. 348. - cclxxxv. 3 ccxxxiv. toni. i. p. 53, 



M M 2 



