EEPTILES. 219 



artery, and the venous branches corresponding to them return their 

 blood to the portal vein\ From this arrangement in serpents, 

 arterial blood also is mixed with venous, and like as in all the 

 reptiles, venous blood is mixed with arterial. 



Tlie ribs of lizards and serpents serve for respiration; in the 

 frogs, which have no ribs, inspiration is eifected by the motions of 

 the tongue-bone. Keeping the mouth closed, they fill its cavity 

 with air through the nostrils; when the nostrils have been closed, 

 they contract the oral cavity, raise the larynx, and press the in- 

 closed air into the glottis. Without closure of the mouth that 

 complete inspiration cannot be effected in batrachians by which 

 the lungs are sufKciently distended^. In the tortoises the same 

 explanation of inspiration has been given, since here the ribs are 

 immoveable. It has, however, been shewn by experiments, that 

 here the inspiration is not effected by deglutition, and that if an 

 opening be made in the trachea it is continued, so that what in 

 other animals is performed by the ribs, is here effected by the 

 moveable belt of the shoulder-bone and clavicle. Expiration is 

 effected partly by contraction of the abdominal muscles, partly by 

 contraction of the lungs themselves. 



In the naked amphibians, the diplopnoa, larynx and trachea 

 form a whole, and in the batrachians this part consists more of 

 larynx, in the proteids more of trachea, that is, in the last it is more 

 developed in length. In Proteus the trachea lias a slip of carti- 

 lage on each side ; of such a slip in the Batrachii the greater part 

 is developed into a cricoid cartilage, or into a cartilaginous ring, 

 representing at once the thyroid and cricoid cartilages ; at its 

 posterior part it has transverse processes, which are afterwards 

 developed into rings of the trachea. Moreover this trachea in 

 batrachians is still entirely membranous, as also are the two 

 bronchi, into which it divides, with the exception of the genus 



1 Cdvier Leg d'Anat. comp. iv. p. 337. The hindmost part of the kings is without 

 vessels. Comp. Htrtl Strcna anatomica de novis pidinonuin vasis in Ophkliis. 

 Pragee, 1837, 4to. 



2 Herholdt shewed the necessity that the mouth should be closed during the 

 inspiration of frogs ; some of his experiments, however, of which the result was, that 

 froo-s when prevented closing the mouth quickly died, have been justly rendered doubtful 

 by RuDOLPHi Ch'U7idriss der Physiologic, 11. a, s. 339. See also on this subject, and on 

 the respiration of tortoises, Haro Ann. des Sc. nat. 26 S^rie, xviii. Zool. 1843, pp. 36 

 — 50, and Panizza ibid, ^ihrne S^rie, ill. 1845, PP- '^3° — 247. 



