348 LUNGS AND DIAPHRAGM CHAP. 



then a larger fourth, after which comes the dilated commence- 

 ment of the small intestine. The latter might be regarded as 

 a chamber of the stomach were it not for the fact that the ducts 

 of the liver and the pancreas open into it. This represents one 

 type of the Cetacean stomach, which seems to be found in all Whales 

 except the Ziphioids. In the latter, the oesophagus opens into 

 the first compartment as usual ; but the second division of the 

 stomach arises not close to the entrance of the oesophagus, but 

 at the opposite end. It would seem, therefore, as if the first 

 division of the stomach, found in most Whales, were missing in 

 Ziphioids. This way of looking at the matter is confirmed by 

 the fact that in Hyperoodon a remnant of the missing first 

 stomach is found in the shape of a small diverticulum of the 

 oesophagus just before it enters the stomach. 



The essential difference between the Whale's and the Eumin- 

 ant's stomach is this : in the latter the stomach is primarily 

 divided into two portions, of which the first is uon- digestive 

 and is clothed with oesophageal epithelium. The second, the 

 abomasum, is the digestive region. The first part is again 

 divided into three compartments. In the Whales, on the other hand, 

 it is the digestive part which is again subdivided, while if the 

 first part is divided it is not markedly so as in the Euminants. 



The lungs are remarkable for their unlobulated character ; in 

 this they agree with the lungs of the Sirenia. The thoracic 

 cavity in which they lie is barrel-shaped, and not, as is usual in 

 terrestrial mammals, boat -shaped, i.e. nairower sternally than 

 above. The alteration of the shape of the thoracic cavity is 

 associated with the aquatic life ; so at any rate the fact that it is 

 also marked in Seals and even in the Otter seems to show. The 

 Whales are also characterised by the great obliquity of the 

 diaphragm, which is extremely muscular. In this character 

 again we find an agreement with the Sirenia, and also with 

 other aquatic mammals ; it is not therefore a character of 

 Whales so much as evidence of an adaptation to the aquatic life. 

 The advantage is, it appears, in the increased capacity of the 

 thoracic cavity, and the consequent greater possibilities of expan- 

 sion of the lungs, which it must be remembered serve as 

 hydrostatic as well as breathing organs. 



Some of the internal arteries of Whales break up into 

 retia mirabilia. Their kidneys are lobulated ; whether this has 



