532 ANATOMY OF VERTEBRATES. 



air during the period occupied by the rotatory transit of the prey 

 to the gullet : it is more probable that at this time the trachea is 

 squeezed flat, and the air in the hinder reservoir of the largest 

 lung may serve to keep up the small amount of respiration needed 

 during the passage of the prey to the stomach, the snake being 

 then at rest and almost torpid. 



In Lizards and Crocodiles certain pairs of vertebral ribs 

 (pleurapophyses) at the forepart of the thoracic-abdominal cavity 

 articulate with sternal ribs (ha3mapophyses), the bony arches being 

 completed by the sternum below. The pleurapophysis, fig. 49, 4 /* 

 (p. 57), forms an angle directed backward at the joint with the 

 hcemapophysis, ib. 6, the muscles raising or drawing outward and 

 forward the upper rib open the angle between it and the lower 

 one; and the head of the rib being fixed to the vertebra, the 

 sternum yields, is depressed, and both the vertical and transverse 

 diameters of the cavity containing the lungs are increased. 

 Consequently the air enters the pulmonary cavities. By the 

 contrary actions, the thoracic-abdominal cavity is contracted, and, 

 the elasticity of the pulmonary parietes aiding, the air is expelled. 



In the Crocodile the increase in the number of the complete 

 sterno-costal arches, fig. 56, i, 2, 3, &c. (p. 68), gives greater effect 

 to their respiratory movements : and the muscular fibres attached 

 to the midriff-like sheets expanded upon the hepatic lobes, may aid 

 in making the general expansion of the thoracic-abdominal cavity 

 tell more directly upon the lungs. 



Almost all the Lacertilia and Batrachia have the peculiarity 

 of inflating their lungs, when they are under the influence of fear 

 or of some other excitement : in the Chameleon, as well as in 

 Polychrus and many other Iguanoids/the expansion of the trunk 

 consequent thereon aids in producing the remarkable change of 

 colours to which we shall recur in the chapter on the integu- 

 ments. 



