300 ANIMAL PHYSIOLOGY, 



it is at an angle of about 30 with the vertical plane. This 

 circumstance, in conjunction with the shortness of the chest, 

 is the cause of the prominent appearance of the abdomen in 

 children. 



The growth of the head deserves especial attention. The 

 maximum proportion of the cranium to the rest of the body 

 is found in the early state of the embryo, and it continues to 

 diminish till maturity is reached. At birth, the parietal 

 region is particularly prominent, while both frontal and 

 occipital regions are comparatively small. During child- 

 hood, the forehead becomes sufficiently developed to produce 

 that projection forwards at the level of the frontal eminences, 

 which gives a characteristic appearance to the child's head ; 

 but these eminences continue to ascend to a higher level 

 above the eyes, and to separate one from the other for a 

 number of years; and the projection forwards of the lower 

 part of the forehead, including the frontal sinus, is not 

 completed till after puberty. A comparatively small de- 

 velopment both of the frontal and the occipital region is 

 characteristic of the female sex. 



The face is exceedingly small in children. It undergoes 

 development in connection with both first and second denti- 

 tion; but it does not reach its full proportions till after 

 puberty, and remains permanently smaller in females than 

 in males. 



The eyeballs and the internal and middle ear are nearly as 

 large at birth as in the adult. 



Probably the period of maximum vital energy is best 

 indicated by the vital capacity of the chest, which is greatest 

 about the age of thirty. As age advances, the diminished 

 rapidity of the pulse, and greater difficulty in repair of 

 injuries, indicate the decline of nutritive activity, and at 

 last, as years accumulate, this becomes insufficient to sup- 

 port the processes necessary for life. 



220. Death. The precise causes of diminished vitality in 

 old age are not known; but it is worthy of note that the 

 corpuscular elements of the tissues have each, apparently, a 

 life of only limited duration, and that they diminish in number 

 as the individual becomes older, being excessively abundant 

 before birth, and most sparingly distributed in old age. Thus 



