I 56 Bulletin American Museum of Natural History. [Vol. XIV, 



respect to the nasals, to be considered presently, it may be said 

 that the palate varies greatly in respect to the ratio of its breadth 

 to its length, and in the relative development and form of its 

 posterior border, the latter varying, especially with age, from a 

 deeply concave to a straight outline; in old age it becomes built 

 out posteriorly by bony deposition, and at the same time tends to 

 become narrower. This change is parallel to the increasing nar- 

 rowness of the skull, with advance in age, at the postorbital con- 

 striction, this region being broader in young adults than in 

 middle-aged specimens, and still narrower in very old examples; 

 for while the skull continues to increase in extreme dimension 

 from middle life onward to old age, the postorbital region be- 

 comes more and more constricted, as is the case generally in 

 animals in which the skull is normally greatly constricted post- 

 orbitally. 



The toothrow tends to become shorter, through normal pro- 

 cesses of absorption, with great increase of age. There is, how- 

 ever, a rather wide range of variation in respect not only to its 

 length, but in the size of the individual teeth in specimens from 

 the same locality, strictly comparable as to sex and age, as shown 

 later in the detailed tables of measurements. While in female 

 skulls the teeth are generally smaller and more delicate than in 

 the males, there are many exceptions to the rule, due to cases 

 of marked individual variation in both sexes. 



The lower jaw is as markedly subject to variation due to growth 

 and age as is the skull in respect to size and the development 

 of the sagittal and occipital crests. This is especially apparent in 

 the angle formed by the coronoid process with the main axis of 

 the jaw. During the evolution of the teeth the last molar appears, 

 as usual, on the inner side of the anterior base of the coronoid, 

 so that when the last lower molar has just come into use its pos- 

 terior border is close to the anterior base of the coronoid. As 

 the growth of the jaw continues after all of the teeth are in place, 

 a space begins immediately to appear between the last molar and 

 the anterior border of the base of the coronoid, which continues 

 to increase with age as long, apparently, as the animal lives, so 

 that in old age the last molar may be 6 to 10 mm. from the front 

 border of the coronoid. With the increase in the length of the 

 jaw, after practical maturity, and the coincident development of 



