388 University of California Publications in Zoology [Vol. '21 



D and E (see figs. 30-33) the condyle projects far behind the angle, 

 but in older skulls the greater posterior projection of the condyle is 

 mvich reduced. The inferior dental foramen comes to be located nearly 

 half way between the condyle and M3. In E it is immediately behind 

 the pocket of M3. The dental foramen likewise moves farther forward 

 on the outside of the mandible. Viewed laterally the chief changes 

 seen in the mandible are those due to the relatively greater increase in 

 depth than in length. As will be seen from figures 28-37 and tables 

 2 and 4 these increases vary greatly in amount. In depth the 

 relative amount of change is greatest in the post-alveolar portion 

 of the mandible. Measurements of the height of the coronoid process, 

 which also reflect the ventral growth of the angular portion of the 

 mandible, show that the increase is 432 per cent whereas the increase 

 in depth of the horizontal ramus is only 272 per cent. From E to Q 

 the portion of the mandible anterior to Pm5 increases in length 87 

 per cent, the tooth row 49 per cetit, and the portion posterior to the 

 tooth row 320 per cent. By far the greatest part of the increase is 

 made behind the tooth row. This is in contrast to the relative amounts 

 of increase in length of the corresponding parts of the cranium. That 

 portion of the cranium anterior tg the tooth row increases 94 per cent 

 from E to Q, which is less than the increase of 77 per cent made during 

 the same time in that portion of the mandible posterior to the tooth 

 row. In both the cranium and the mandible, however, there is a pro- 

 portionately smaller amount of increase in the length of the maxillary 

 tooth rows than there is in the portions either anterior or posterior 

 to them. Comparisons of amounts of increase in depth in these three 

 corresponding regions of the cranium and mandible show that the 

 greatest relative amounts of increase occur in the post-alveolar portion 

 of the mandible and in the pre-alveolar portion of the cranium. The 

 least relative amounts occur in the pre-alveolar portion of the mandible 

 and in the post-alveolar portion of the skull. In depth the relative 

 amount of increase in the alveolar regions of both the cranium and 

 the mandible is intermediate in amount. The depth measurements of 

 the skull are the three depth measurements given in table 2. The 

 percentages of increase from posterior to anterior are: 90, 96 and 188. 

 The post-alveolar and alveolar depth measurements of the mandible 

 are given in table 4. The pre-alveolar depth measurement was taken 

 at the point of least depth in the diastema of the mandible. The ])er- 

 centage of increase in depth of the mandible at these three points 

 from posterior to anterior are : 432, 272 and 64. From figures 38-39 

 it will be seen that the mandible straightens with increased age. The 



