CHAPTEK XVIII. 



DEVELOPMENT OF THE BODY AFTER BIRTH. 



THE newly-born infant is still far from having arrived at a state of 

 complete development. The changes through which it has passed while 

 in the foetal condition are followed by others during the periods of 

 infancy, childhood, and adolescence. The anatomy of the organs, both 

 internal and external, their physiological functions, and even the morbid 

 derangements to which they are subject, continue to undergo gradual 

 and progressive alterations, throughout the entire course of subsequent 

 life. The history of development extends, properly speaking, from the 

 earliest organization of the embryonic tissues to the complete formation 

 of the adult body. The period of birth marks only a single epoch in a 

 constant series of changes, some of which have preceded, while many 

 others are to follow. 



The weight of the newly-born infant is about seven pounds. The 

 middle point of the body is nearly at the umbilicus, the head and upper 

 extremities being still large, in proportion to the lower extremities and 

 the pelvis. The abdomen is larger and the chest smaller, in proportion, 

 than in the adult. The lower extremities are still partially curved in- 

 ward, so that the soles of the feet look obliquely toward each other, 

 instead of being directed horizontally downward, as at a subsequent 

 period. Both the arms and the legs are curled upward and forward 

 over the chest and the abdomen, and all the joints are in a semi-flexed 

 position. 



The process of respiration is imperfectly performed for some time 

 after birth. The expansion of the pulmonary vesicles, and the changes 

 in the circulatory apparatus which take place at the time of birth, far 

 from being instantaneous, are always more or less gradual in character, 

 and require an interval of several days for their completion. Respira- 

 tion seems to be accomplished, during this period, to a considerable ex- 

 tent through the skin, whicli is remarkably soft, vascular, and ruddy. 

 The animal heat is less actively generated than in the adult, and re- 

 quires to be sustained by careful protection, and by contact with the 

 body of the mother. The young infant sleeps during the greater part 

 of the time ; and even when awake exhibits comparatively few mani- 

 festations of intelligence or perception. The special senses of sight 

 and hearing are dull and inexcitable, and even consciousness seems 

 present only to a limited extent. Voluntary motion and sensation are 

 52 ' ( 809 ) 



