CHAPTER XVII. 

 DEVELOPMENT OF THE BODY AFTEE BIRTH. 



ITIHE newly-born infant is still far from a condition of complete de- 

 J- velopment. The changes through which it has passed in fetal life 

 are followed by others during infancy, childhood, and adolescence. 

 The anatomy of the organs, their physiological functions, and even 

 the morbid derangements to which they are subject, continue to 

 undergo progressive alterations throughout the whole course of sub- 

 sequent 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 is only a single 

 epoch in a long 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 

 limbs being still large, in proportion to the lower limbs and pelvis. 

 The abdomen is larger and the chest smaller, in proportion, than in the 

 adult. The lower limbs are still partially curved inward, so that the 

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

 directed horizontally downward, as at a subsequent period. The arms 

 and legs are curled forward over the chest and 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 accom- 

 panying changes in the circulation at birth, far from being instanta- 

 neous, are more or less gradual, requiring an interval of several days 

 for their completion. Respiration seems to be accomplished, during 

 this period, to a considerable extent through the skin, which is soft, 

 vascular, and ruddy. The animal heat is less actively generated than 

 in the adult, and requires 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 when awake exhibits but 

 few manifestations of intelligence or perception. The special senses 

 are comparatively inexcitable, and even consciousness seems present 

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

 absent ; and the almost constant irregular movements of the limbs, 

 observable at this time, are mainly automatic. Nearly all the nervous 

 phenomena presented by the newly-born infant, are of a similar nature. 

 The motions of its hands and feet, the act of suckling, and even its 

 cries and the contortions of its face, are reflex in origin, and do not 



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