1926] Hall: Slull of the Bodent OtospcrmopMlus grammurus hecclieyi 397 



This is especially true of the palatal width. The statement of Howell 

 (1924, p. 994) concerning Microtus, that: "In considering the varia- 

 tion of the skull with age, the anterior ring, chiefly the frontals, of the 

 cranium is 'dead center,' from which there is development anteriorly 

 and posteriorly, ' ' and the statement of Taylor (1918, p. 440) , regarding 

 ApJodontia^ that : "Through all of these changes the distance anteriorly 

 across the palate between the alveoli of the fourth premolars remains 

 practically constant," coupled with my own observations on other 

 mammals, leads me to believe that a well developed palatal region at 

 birth is a rather constant feature in the Eutheria and perhaps in the 

 class Mammalia. Of the several regions of the head, the buccal cavity 

 is, as directly if not more directly than anj^ concerned with the inges- 

 tion of food, from the time of birth until the end of the nursing period. 

 The width of this cavity is reflected in the width of the palate. 



It was pointed out that the greatest amount of increase occurring 

 in any one of the four periods recorded in table 5, in the postorbital 

 region of the skull, occurred in the first, that is, between C and E. 

 The increase in the measurements of the postorbital region, especially 

 in early stages, reflects the increase in size of the brain. The size of 

 the brain is more directly indicated, however, by the weight of number 

 12 shot required to fill the cranial cavity. From D to Q inclusive the 

 weights, in grams, of the shot required to fill the cranial cavities are 

 as follows: 3.0, 7.6, 14.7, 19.1, 27.8, 27.0, 29.6, 33.7, 35.8, 34.8, 36.2, 

 34.8, 36.9, and 38.4. In these weights, as in the measurements of the 

 post-orbital portion of the skull, the greatest per cent of increase occurs 

 between C and E. In fact, there is a greater per cent of increase in 

 weight of number 12 shot required to fill the cranial cavity between D 

 and E than in any of the other four stages designated in table 5. 

 Weighing the shot was found to be more accurate for comparative pur- 

 poses than measuring the shot by cubic centimeters. Does not this 

 relatively great development of the brain at so early a stage reflect 

 what might be expected, namely, that the animal would require an 

 early development of the organs which permit it to direct and control 

 its reactions to its environment to the end of its greatest good "? It was 

 also pointed out that the part of the skull housing the brain increases 

 less after birth than the rostral portion of the skull. This would seem 

 natural, since we know that at the very hour of birth some reactions to 

 environment, presumably having their seat in the brain, are required 

 of the animal if it retains its hold on life. The fact that the precocious 

 development of the brain is due to the necessity for complete early 

 development of nervous tissue is not overlooked here. Granted that 



