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. 
Fig. 388.—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 1933, 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, ze., with many transverse 
ridges. If we start with the multitubercular tooth and 
gradually form a number of transverse ridges by union 
