142 



THE FROG 



irregular honeycomb. All these ridges are abundantly 

 supplied with blood-vessels fed by the pulmonary artery, the 

 blood being carried away by the pulmonary vein. 



The main substance of the lung is made of connective- 

 tissue containing elastic fibres and unstriped muscle, and 

 traversed by a network of capillaries. Its cavity is lined 

 by a layer of pavement-epithelium, and its outer surface 

 is covered with peritoneum. 



Respiratory Movements. In breathing, the frog depresses 

 the floor of the buccal cavity (Fig. 45, A), and, the mouth 



A 9l 



p.c.hy 



ring. 



FIG. 44. The respiratory organs of the frog from the ventral aspect ; B, the laryngo- 



tracheal chamber in longitudinal section, with the right lung. 



ar. the arytenoid, or principal cartilage of the larynx ; b. hy. body of hyoid ; gl. 

 glottis ; /. Ing. left lung ; /. tr. c. laryngo-tracheal chamber ; /. c. hv. posterior 

 horn of hyoid ; r. Ing. right lung, laid open in A to show its internal surface ; 

 v. cd. vocal cord. (After Howes). 



being kept shut, air is drawn in through the nostrils. The 

 floor of the mouth is then raised (.B} by muscles attached 

 to "the hyoid. At the same time the anterior end of the 

 lower jaw presses upon the movable premaxillae (pwx), the 

 upward processes of which (p. 42, Figs. 8 and 9, PMX) act 

 upon certain cartilages in connection with the external 

 nostrils in such a way as to produce closure of these 

 apertures (Fig. 45, }. The gullet (gul) is so contracted, 

 except during the act of swallowing, as to be practically 



