THE ENTIEE SKULL 495 



and eighty-six days old. Six cats were from two litters of another 

 mother. From the spring litter were taken those one, ninety, and one 

 hundred and twenty days old ; from the summer litter, those three, 

 fifteen, and thirty-five days old. The remaining cats were from dif- 

 ferent litters of different mothers. It will be noticed in the table (page 

 506) that the skull of the cat eighty days old is smaller than several 

 of the younger skulls ; this was owing to the unfavorable conditions 

 under which the animal was reared ; to particularly favorable con- 

 ditions must be attributed the greater development of the skull of the 

 cat sixty days old. Hence it must not be supposed that every cat will 

 present, at the age given, the exact degree of cranial development 

 illustrated in the figures ; these are introduced to enable the student to 

 fix approximately by cranial characters the age of kittens before the 

 eruption of the permanent dentition. I have begun the series with the 

 skull shortly before birth ; it is possible that some kittens at birth may 

 present no greater cranial development than was therein observed. 



The general changes which take place in the skull from birth to 

 adult life are, increase in size, changes in form and in the relative 

 proportions of different parts, and the gradual ossification of cartilagi- 

 nous and membranous portions. 



The increase in length (page 506) from the opisthion, on the pos- 

 terior rim of the foramen magnum, to the alveolar point, on the al- 

 veolar border of the premaxillaries, is from thirty to seventy-nine 

 millimetres ; the increase in cranial height, measured on the inside of 

 the cranial cavity from the suture between the presphenoid and basi- 

 sphenoid to the bregma, at the junction of the sagittal and coronal 

 sutures, is from fifteen to twenty-six millimetres. As the skull in- 

 creases in length, the length of the face relatively to the length of 

 the whole skull increases and the relative length of the cranium 

 decreases. The relations may be shown by the facial length index 



/facial length X 100\ wMch before birth ig 3Q and at adult Hfe ig 4Q 5 . 

 V length of skull / 



/cranial length X 100\ , . , 

 and by the cranial length index ^ -- ; . ' , -- j, which before 



birth is 66.6 and at adult life is 55.6. 



It will be observed that in the younger skulls the anterior part of 

 the cranium presents prominent frontal eminences, below which the 

 profile of the face is concave ; as the skull develops, these eminences 



