DEVELOPMENT OF THE INFANT. 247 



an object high up, is a late development in the 

 infant, and indicates the advance of intellectuality.* 

 It is noteworthy that in hydrocephalus the eyes 

 frequently roll upwards, but the eyelids remain 

 drooped, hiding the cornese. 



In the list given above, which is by no means 

 complete, the order followed is about that in which 

 the development of these signs takes place. We 

 will now attempt some kind of physiological classi- 

 fication. Some of these nerve-muscular signs 

 follow and result from external agencies. Thus, 

 turning towards a light or an object depends upon 

 light passing from these things to the child's eyes 

 and brain ; ( turning to a sound is the direct effect 

 of the sound-undulations of the air. So, again, 

 when movement is checked or altered by "the 

 sight of an object" or "a sound," the result is 

 the effect of the waves of light, or of air upon the 

 nerve-mechanism ; in every healthy brain the effect 

 of such waves is probably nearly identical. Other 

 motor signs are more directly intrinsic, the physio- 

 logical outcome of the structure and properties of 

 the nerve-mechanism, thus: crying, reflex actions, 

 parallelism in the movements of the eyes, the 

 constant movement of the fingers and limbs while 

 the infant is awake, some movements of expression 

 in the face, playfulness ; and later on, the repetition 

 of identical movements upon similar stimulation, 

 the acquired power of co-ordinating movements of 

 the hand ; and still later, the power of using both 



* Chap. xii. p. 223. t See chap. x. p. 185. 



