LUNGS OF REPTILES. 



523 



349 



long trunk ; and the ciliated tracts upon the inner surface begin 

 to be raised therefrom, and to mark out shallow depressions 011 

 the vascular surface, at least along the anterior half of the sac. 

 In the Axolotl, in which the lungs terminate at the hinder third 

 of the abdomen, the alveolar depressions or cells are more marked. 

 In the Amphiume the lungs are narrow, and terminate in a point, 

 within a short distance of the anus : on the inner surface elastic 

 bands are developed in the inter-alveolar partitions, and the alveoli 

 begin to be subdivided into smaller cells. In the Menopome the 

 lungs have a similar structure, but are proportionally smaller, and 

 with larger alveolar depressions. 



The lungs of the Frog, fig. 349, are wider in proportion to 

 their length, and extend along the 

 dorsal part of the abdominal cavity, 

 with the vertebral bodies and vascu- 

 lar trunks intervening. They are 

 continued by short bronchia? or bron- 

 chial apertures, fig. 350, f, directly 

 from the larynx. The proper tissue 

 of the bag is composed of very elastic 

 fibre, covered by peritoneal epithe- 

 lium, and lined by the capillary net- 

 Avork and its epithelial covering ; 

 the pulmonary artery takes its course 

 beneath the peritoneal layer, the pul- 

 monary vein runs beneath the inter- 

 nal epithelium ; the one on the fore 

 and outer part, the other nearer the 

 inner or mesial side of the lung. The 

 whole inner surface is honeycombed, 

 and the alveoli are subdivided into 

 smaller cells. The arterioles run 

 along the attached borders of the septa, the venules along the 

 free borders. The ciliary epithelium is limited to the margins 

 of the alveoli supporting the larger venules: the capillary net- 

 work, covered by non-ciliated delicate epithelial scales, is 

 disposed upon the sides and bottom of the ultimate cells, the 

 septa having a layer of the capillary network on each side. 

 Thus the lungs of the tailless Batrachia, and more especially of 

 the Pipa, in which they are very broad and the bronchial tubes 

 long, have a more extensive respiratory surface in proportion to 

 their size than in the tailed species. 



But the pulmonary artery is not exclusively distributed to the 



Heart and lungs, Frog. CCLXTIII. 



