ORGANIZATIONOFREPTILES. 25 



malia; there, it is effected by the agency of the diaphragm, the ribs, and intercostal 

 muscles; here it is produced by an arrangement of the parts about the neck, and 

 by the abdominal muscles. The lingual bone is drawn down by the muscles 

 coming from the stermun; this enlarges the cavities of the mouth and fauces; air 

 rushes in through the nares, which are afterwards closed; the lingual bone is then 

 elevated, and the air is forced through the glottis and trachea to the lungs. The 

 process therefore, consists of the deglutition or swallowing of air, instead of its 

 inspiration, as in Mammalia; and this mechanism explains to us why the lungs do 

 not collapse when the cavity of the chest is opened; and even should they be 

 compressed, the animal has the power of inflating them again, as long as the parts 

 about the mouth and larynx remain perfect. In the Sauria, respiration is aided 

 by ribs, movable on the spine, and united in front to each other, or with a sternum 

 of greater or less extent. In Serpents, as in the Sauria, respiration is assisted by 

 ribs and abdominal muscles; but here the anterior extremity of the ribs is always 

 free and unconnected, and their mode of attachment to the spine, by elastic hga- 

 ments, allows considerable dilatation, and they can be drawn together by means 

 of the intercostal muscles. The ribs, in this class, besides aiding in respiration, 

 are instruments of progression, the animal advancing them, when in motion, like 

 the legs of caterpillars.* In the Batrachia, no ribs are employed in respiration; 

 they are either entirely wanting, or are too short to have any effect. 



Physiology of Respiration. — The immediate effect of this function is to convert 

 the venous into arterial blood, in order to fit it for nutrition. The colour of the 

 blood is changed in the cells of the lungs; its temperature is elevated, and in the 

 higher classes its tendency to coagulation is very much increased; and there is no 

 doubt that a similar change takes place in the lungs of Reptiles; not so complete, 

 however, because only a portion of the blood is offered to the lungs. The respi- 

 ratory organs may be regarded also as the principal source of animal heat, the 

 temperature being most elevated in those animals where respiration is most perfect. 

 Where most blood is exposed to the air in the lungs, as in man, its temperature 



* Home's Lect. Comp. Anat., vol. i. p. 115. 

 Vol. I.— 4 



