BREATHING AND HISSING OF SNAKES. 143 



tion is comparatively languid, the reptile becomes easily 

 torpid, and its temperature is influenced by the surrounding 

 atmosphere more than by the vigour of its own functions. 

 This is why, when not excited to activity by external 

 warmth, reptiles can pass a long time without food. Having 

 no fixed temperature to maintain, one important source of 

 demand for food is withdrawn. 



The air enters their lungs chiefly in a direct course from 

 the nostrils, only by the mouth when open. If you observe 

 the flatness of the head, and the very short space that can 

 exist between the nose and the mouth of snakes, you will 

 readily trace the communication between the entrance to 

 the trachea and the outer air through the nostrils when the 

 glottis is not closed. Professor Owen, in his Anatomy of 

 the Vertebrates, vol. i. p. 528, describes this process fully. 

 In the foregoing description I have borrowed from him, 

 as well as from Dr. Carpenter, Todd, and others ; but as 

 there is nothing like ' seeing for oneself,' I would persuade 

 my readers to watch a snake for a few minutes. An in- 

 spiration at intervals will be easily discerned by the expan- 

 sion of the body. You will also perceive partial or slighter 

 breathings, and the trunk dilating and expanding gently 

 through a sort of internal respiration which is going on ; 

 every now and then comes the deeper, fuller breath. 



You may perceive that sometimes one short portion of 

 the body expands, as if the lung in that part only were 

 at work. This is more easily seen in the larger snakes. 

 I have watched these for a quarter of an hour or more at 

 a time, during which period only a comparatively short 

 portion of the body showed any signs of breathing. 



