554 ORGANS OF RESPIRATION. 



The reptiles breathe solely by means of pulmonary cavities, 

 no branchiae having been hitherto detected in any condition 

 of animals higher than amphibia, and the thick scaly cover- 

 ings of serpents, saurians, and chelonians, preventing respi- 

 ration through their skin. The form of the lungs of reptiles 

 as that of their other organs, accords with the general form 

 of the body, being long simple sacs in the serpents, broad 

 cellular organs expanded over the whole dorsum of the trunk 

 in chelonia, and approaching nearer to the mammiferous 

 type in the higher sauria. The want of bilateral symmetry 

 in the pulmonary organs, often produced in quadrupeds by 

 the sinistral position of the heart, is greater in serpents than 

 in all other vertebrata, as they are here sometimes developed 

 only on one side of the body, and that the right, on which 

 side alone they exist in the highest pulmonated invertebrata, 

 the air-breathing gasteropods, and on which side they are 

 largest in the mammalia. In many saurians also the right 

 lung is much larger than the left. These proportions of the 

 two lungs, however, appear to be reversed in some ophi- 

 dian reptiles, without the law of this variety being apparent. 



The lungs of serpents are generally composed of two une- 

 qual, long, narrow, cylindrical or fusiform sacs, extending far 

 back in the cavity of the abdomen, above the other viscera, 

 surrounded with the serous lining of that cavity, without 

 internal cellular divisions, excepting at the dorsal portion of 

 their anterior end. In different species of coluber, typhlops, 

 and vipera, the lung of one side only is developed, and in 

 other genera, as boa and python, they are developed nearly 

 equally on the two sides. They communicate by a long 

 narrow, single, firm, annulated trachea, surrounded by dis- 

 tinct, though incomplete rings, with the back part of the 

 tongue, where the larynx already presents the aryteenoid, 

 cricoid, and thyroid cartilages, and is sometimes fur- 

 nished with a distinct epiglottis, as shown by Henle in the 

 large crotalus durissus. The annulated marking of the 

 almost membranous trachea, is sometimes, as in python, 

 continued perceptibly over the long cylindrical pulmonary 

 sacs. On opening the lungs of the boa or python, as in 

 most other ophidia, a beautiful cellular and highly vascular 

 appearance is presented in the interior of the upper and back 

 part of these organs, somewhat resembling the interior 

 polygonal cells of the second stomach of ruminantia, and 



