1904.]- 



ANATOMY OF PELAGIC SERPEXTS. 



153 



surface of the lung is inai'ked by conspicuous tliickenings ; l)ut 

 these flo not form a honeycomb network as in Platyurus. 



Tlie folds run across the lung — that is at i-ight angles to its longi- 

 tudinal axis, and are wavy in outline, which of coui-se allows of 

 expansion during inspiration (text-fig. 27, p. 152). The trachea (or 

 lironchus) is continued as a gutter down the lung as far as the com- 

 mencement of the Kver, that is for a very short distance behind 



Text-fis-. 28. 



A ijortioii of the inteiiial surface of the noii-\ asculur part of tlie lung ot 

 ILydrus plati/uras. 



the heart. I The lung itself is extraordinarily long ; it is indeed 

 co-extensive with the body-cavity, reaching as far back as the vent. 

 Its calibre too is very considerable, and its '\\'alls have the tough, 

 almost shiny, appearance of a fish's swim-bladder. The dorsal wall 

 is firmly fixed to the parietes. The latter part of the lung, /. e. after 

 the end of that region which is resj)iratory, has undei'gone some 

 modification in i-elation to its undoubted function as a swim- 

 bladder. The folds already spoken of in the vascular region of 

 the lung persist ; but their object is no longer that of merely 

 increasing the i-espii'atory surface, and thus the efficiency of the 

 lung as a breathing oi'gan. They exist only as bands of muscular 

 fibre, which, since their dii-ection is mainly cii'cular and parallel 

 to each other, must act as constrictors and expel air from 

 the swim-bladder part of the lung. On a naked-eye inspection of 

 this portion of the lung, it looks almost as if the bands in question 

 were the bronchial rings which had in this i-egion taken on a 

 new development. They are, howevei', serially continuous not 



