MAMMALIA. 



569 



The proboscis forms a *' limb " capable of almost any 

 diversity of movement and function. Its presence and use 

 involves a shortening of the neck and a raising of the 

 occipital crest of the skull. This is effected by the growth 

 of a mass of bone, lightened by a number of enclosed air 

 sinuses. In this manner the muscles for raising the head, 

 inserted in the occipital region of the skull, obtain sufficient 

 leverage to support the weight of the trunk and tusks. 

 These latter are true incisors, though during development 

 they move from the premaxillary to the maxillary region. 



I'ig- 3S8. — Surface Views of a Single Molar Tooth of 

 (A) THE African and (B) the Indian Elephant. 



Note the polylophodont enamel ridges in each, worn by attrition into flat crests. 



They have a tip of enamel which is soon worn off and 

 the tusk then consists of dense ivory or dentine. 



The molar teeth consist of a vestigial first premolar, only 

 found occasionally, and six others, or making a normal 

 dentition of \%%%, but each tooth is of enormous size and 

 they succeed each other in horizontal succession, only two 

 being generally in use at the same time. There appears to 

 be no milk-series, hence the Proboscidea are monophyodont. 

 Each tooth is polylophodont, i.e., with many transverse 

 ridges. If we start with the multitubercular tooth and 

 gradually form a number of transverse ridges by union 



