DEVELOPMENT OF THE BODY AFTER BIRTH. 687 



CHAPTER XVIII. 



DEVELOPMENT OF THE BODY AFTER BIRTH. 



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

 state of complete development. The changes through which it has 

 passed during intra-uterine life are not more marked than those 

 which are to follow during the periods of infancy, childhood, and 

 adolescence. The anatomy of the organs, both internal and ex- 

 ternal, their physiological functions, and even the morbid derange- 

 ments 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, accordingly, 

 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 a little over six pounds. 

 The middle point of the body is nearly at the umbilicus, the head 

 and upper extremities being still very large, in proportion to the 

 lower extremities and pelvis. The abdomen is larger and the 

 chest smaller, in proportion, than in the adult. The lower extremi- 

 ties are curved inward, as in the foetal condition, so that the soles of 

 the feet look obliquely toward each other, instead of being directed 

 horizontally downward, as at a subsequent period. Both upper 

 and lower extremities are habitually curled upward and forward 

 over the chest and abdomen, and all the joints are constantly in a 

 semi-flexed position. 



The process of respiration is very imperfectly performed for 

 some time after birth. The expansion of the pulmonary vesicles, 

 and the changes in the circulatory apparatus described in the pre- 

 ceding chapter, far from being sudden and instantaneous, are 

 always more or less gradual in their character, and require an 

 interval of several days for their completion. Respiration, indeed 



