MAMMALIA. 547 



The molar teeth of elephants consist of many (up to twenty- 

 four) successive ridges, each with its roots. Hence it is 

 possible, by an appeal to the principle of cusp-multiplica- 

 tion followed by separation, to suggest an origin for the 

 great number, as well as the simple structure of the ceta- 

 ceous teeth. 



Behind the mouth the larynx and glottis are produced 

 from the ventral wall of the oesophagus upwards as a long 

 cylinder into the base of the internal nostrils, a striking 

 adaptation which enables the porpoise to open its mouth 

 under water and even to swallow whilst breathing. A 

 similar modification is found in young Metatheria, in this 

 case enabling them to breathe and swallow milk at the same 

 time. 



Returning to the porpoise we find that it possesses a 

 complex stomach, a rare possession for a flesh-eater. The 

 first and largest chamber is a storage sac w^ith no glands, 

 probably a mere dilatation of the oesophagus : this is 

 followed by a smaller receptacle with fundus (tubular) 

 glands and folded walls : a very small globular third 

 compartment passes into a long vermiform fourth part 

 which has pyloric glands and leads into the duodenum. 



Reverting to the skeleton, we find the cervical vertebrae, 

 seven in number, are short and fused together. A flexible 

 neck, far from being a necessity, is rather a drawback to an 

 aquatic animal, rigidity of the anterior end being imperative 

 for rapid locomotion. The dorso-lumbar vertebrae are hard 

 to define for there is no sacrum, but between the first 

 caudal and the last cervical there are about twenty-seven in 

 number, the first thirteen, as in most mammals, bearing 

 ribs. The transverse processes are prominent, as also are 

 the neural spines. The former arise from the side of the 

 centrum in the last lumbar, but higher and higher up on the 

 neural arch as one proceeds forwards. The round disc- 

 shaped epiphyses are very conspicuous. The hindermost 

 of these dorso-lumbar are probably the former sacral verte- 

 brae, but as the ilia have atrophied there is no certainty. 



The caudal vertebrae are numerous (30-31) and, as in 

 the kangaroo, bear paired chevron bones on their under 

 surface. It is usually assumed that the caudals commence 

 with the chevron bones. The fore-limb and girdle are 



