440 THE VERTEBRATE SKELETON. 



In the Walrus the upper canines form immense tusks. The 

 other teeth are all small and one-rooted, and the molars have 

 flat crowns. In the true seals the dentition is strikingly pis- 

 civorous, the cheek teeth often having accessory cusps (fig. 86). 



The INSECTIVORA are diphyodont and heterodont, having 

 well-developed rooted teeth. The canines are usually weak, 

 the incisors pointed, and those of the two jaws often meet 

 like a pair of forceps. The crowns of the molars are charac- 

 teristically studded with short cusps. Some genera, such as 

 Gymnura and the mole, Talpa, have the regular mammalian 

 dentition. In the hedgehog, Erinaceus, the dentition is 



i - c ^ pm - m -, total 36. 



In the genus Sorex (Shrews) the teeth differ in the following 

 two marked respects from those of most other Monodelphia, 

 (1) they are monophyodont, (2) the lower incisors sometimes 

 become fused to the jaws. Most Insectivora have square molar 

 teeth, but in Potamogale, Chrysochloris, Solenodon and the 

 Centetidae the molar teeth are triangular in section. Four 

 molars occur in Centetes. 



In the aberrant genus Galeopithecus the dentition is 

 91 23 

 i ^ c = pm - m K , total 34. The upper incisors are placed at 



G 1 2i O 



some distance from the anterior end of the jaw, and the outer 

 upper incisors and canines of both jaws have two roots, a 

 very unusual character. The lower incisors are deeply grooved 

 or pectinated in the same way as are the lower incisors of Pro- 

 cavia. The upper incisors and canines of both jaws bear many 

 cusps, and are very similar in appearance to the cheek teeth of 

 some Seals. 



The dentition of the CHIEOPTERA is diphyodont and hetero- 

 dont, and the dental formula never exceeds 



21 33 

 i g c - pm g m 3 ' total 38 - 



