MAMMALIA PACHYDKRMATA, 519 



well as on herbage, and succulent roots, its 

 organs of mastication are powerful, and its 

 teeth of great size. The whole of this apparatus 

 requires an immense developement of bone to 

 render it efficient ; so that the head, with its 

 huge tusks and grinders, is of enormous weight. 

 Had this ponderous head been suspended at the 

 end of a neck of such length as to admit of its 

 being carried to the ground, as is the case in 

 grazing animals, it would have destroyed the 

 balance of the body, and would have required 

 greater force to raise and retain it in a hori- 

 zontal position than was competent to any 

 degree of muscular power. Nature has accord- 

 ingly abandoned this form of structure, and 

 has at once curtailed the neck, bringing the 

 head close to the trunk of the body, and sup- 

 porting it by means of short, but powerful 

 muscles, which are not implanted in any par- 

 ticular point of the skull, as they are in other 

 quadrupeds, where the occipital bone forms 

 a crest or ridge for that purpose ; but the 

 general surface of the cranium has been en- 

 larged by an immense expansion given to its 

 interior cellular structure, and thus the muscles 

 are attached to a considerable extent of bone, 

 instead of being affixed to a single process, 

 which would have incurred great risk of being 

 broken off by their action. These large cells 

 are constructed with a view to combine strength 



