LUNGS. 



ALIMENTARY CANAL. 



557 



continuous passage between the narial passage and the larynx. 

 The trachea is very short, and gives off a third bronchus to the 

 right lung just before it divides. The lungs are very spacious 

 and not lobed ; they extend, like the swimming bladder of fishes, 

 far backward, and play an essential part in the maintenance of 

 the horizontal position in water. The diaphragm also has a 

 corresponding horizontal extension, as it has in the Sirenia. 

 The stomach is complicated and divided into three or more 

 chambers. In Phocaena (Fig. 287) the oesophagus opens into 

 a large elongated blind sac lined by a thick epithelium ; near the 

 oesophageal end 

 of this is the 

 opening into the 

 second chamber, 

 the lining of 

 which is soft and 

 vascularand pro- 

 jects in longitu- 

 dinal folds into 

 the cavit3^ The 

 third chamber is 

 tubular, and pos- 

 sesses a small 

 globular dilata- 

 tion at its com- 

 mencement ; it 

 opens into the 

 duodenum, the 

 c o m m e ncement 

 of which is dilated and receives the conjoined bile and pan- 

 creatic ducts. In Ziphioids * the first chamber is absent, or 

 combined with the second, and the pyloric chamber is divided 

 up into seven or eight chambers by successive constrictions. 



There are saccular dilatations on the aorta and puhnonary 

 arteries, and retia mirabilia on the arteries, particularly those 

 under the pleura and between the ribs, and on the veins. The 

 use of these is not understood, but they are supposed to be 

 connected in some way with the power these animals have of 



Fig. 2S7. — Diagrammatic section of the stomach of a porpoise 

 (from Flower and Lydeklcer). a oesophagus b cardiac ch.im- 

 ber, c middle chamber, d and e two divisions of the third or 

 pyloric chamber, / pylorus, g duodenum, h bile-duct. 



* Jungklaus, Jen. Zeitschr., 32, 1898, p 



