644 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



the weight. The toes are not separate, but are embedded in the com- 

 mon mass of the cylindrical foot, the hoofs being represented by nails 

 around its forward margin. These may be fewer in number than 

 the toes. 



ADAPTATIONS OF THE SKULL AND TEETH. 



Owing to the shortness of the neck and the height of the head from 

 the ground, the proboscis or trunk, which is merely an elongation 

 of the combined nose and upper lip, becomes a most necessary device 

 for securing food and water. This organ is composed of a great 

 number of muscles, and so combined and controlled as to give not 

 only enormous strength but the utmost delicacy of movement. The 

 trunk terminates in one (Indian) or two (African elephant) finger- 

 like projections, with which a pin can be picked up from the ground, 



while the entire organ 

 has sufficient strength to 

 uproot a tree. 



The development of 

 the trunk has been ac- 

 companied by a marked 

 change in the character 

 and form of the skull, 

 which is merely a me- 

 chanical adaptation to 

 provide the leverage nec- 

 essary to wield so 

 weighty an organ. This 

 has been brought about 

 by a shortening of the 

 skull, accompanied by a 

 corresponding increase in height. The result is that the base of 

 the trunk has been brought much nearer the fulcrum at the neck, 

 thus shortening the weight arm of the lever, while the increasing 

 height not only lengthens the power arm, but gives more surface 

 for the attachment of muscles and the great elastic ligamentum 

 nuchse which aids in supporting the head. 



This change in the form of the skull, while it gives to the physi- 

 ognomy of the animal that dignified, intellectual look, does not imply 

 a similar development of the brain, for the brain case has increased 

 but little, the great size of the skull being largely due to the develoj)- 

 ment of air cells in the cranial bones, so that the actual thickness of 

 the roof of the skull is greater than the height of the brain chamber 

 itself, a feature well shown in figure 4. 



Fig. 3. — American mastodon ; after Owen. 



