810 DEVELOPMENT OF THE BODY AFTER BIRTH. 



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 their origin, and do 

 not indicate the existence of active volition, or distinct perception of 

 external objects. There is at first but little nervous connection with 

 the external world, and the system is almost exclusively occupied with 

 the functions of nutrition and respiration. 



The difference in organization between the newly-born infant and 

 the adult may be represented, to some extent, by the following list, 

 which gives the relative weight of the most important internal organs 

 at the period of birth and in adult age ; the weight of the entire body 

 being reckoned, in each case, as 1000. The relative weight of the adult 

 organs has been calculated from the estimates of Cruveilhier, Solly, and 

 Wilson, that of the organs in the foetus at term from our own observa- 

 tions. 



Foetus at term. Adult. 



Weight of the entire body . . . 1000.00 1000.00 



" encephalon . . . 148.00 23.00 



" liver .... 37.00 29.00 



" heart .... 7.77 4.17 



" " kidneys .... 6.00 4.00 



" supra-renal capsules . 1.63 0.13 



" thyroid gland . . . 0.60 0.51 



" thymus gland . . . 3.00 0.00 



It appears that most of the internal organs diminish in relative size 

 after birth, owing principally to the increased development of the osse- 

 ous and muscular systems, both of which are in an imperfect condition 

 throughout intra-uterine life, but come into activity during childhood 

 and youth. 



The remains of the umbilical cord begin to wither within the first day 

 after birth, and become completely desiccated by about the third day. 

 A superficial ulceration then takes place at the point of its attachment, 

 and it is separated and thrown off within the first week. After the 

 separation of the cord, the umbilicus becomes completely cicatrized by 

 the tenth or twelfth day. (Guy.) 



An exfoliation and renovation of the cuticle take place over the whole 

 body soon after birth. According to Kolliker, the eyelashes, and pro- 

 bably all the hairs of the body and head, are thrown off and replaced 

 by new ones within the first year. 



The teeth in the newly-born infant are but partially developed, being 

 still inclosed in their follicles and concealed beneath the gums. They 

 are twenty in number, namely, two incisor, one canine, and two molar 

 teeth on each side of each jaw. At birth there is a thin layer of den- 

 tine and enamel covering their upper surfaces, but the body of the tooth 

 and its fangs are formed subsequently by progressive elongation and 



