DEVELOPMENT OF THE BODY AFTER BIRTH. 705 



indicate any active volition, or distinct perception of external objects. 

 There is but little nervous connection with the external world, and the 

 system is occupied almost exclusively with the functions of nutrition 

 and respiration. 



The difference in organization between the newly-born infant and 

 the adult is represented, to some extent, in the following list, which 

 gives the relative weight of the most important organs at the period 

 of birth and in adult age ; the weight of the entire body being reck- 

 oned, in each case, as 1000. The relative weight of the adult organs 

 is calculated from the estimates of Cruveilhier, Solly, and Wilson, that 

 of the organs in the foetus at term from our own observations : 



Foetus at term. Adult. 



Weight of the entire body . . . 1000.00 1000.00 



u encephalon . . . 148.00 23.<>u 



" liver .... 37.00 29.00 



" heart .... 7.77 4.17 



u kidneys .... 6.CO 4.00 



" supra-renal capsules . 1.63 0.13 



" thyroid gland . . 0.60 0.51 



u 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 

 osseous and muscular systems, both of which are very imperfect 

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

 and youth. 



The remains of the umbilical cord begin to wither within twenty- 

 four hours after birth, and become completely desiccated by about the 

 third ckv. A superficial ulceration then takes place at its point of 

 attachment and it is thrown off within the first week. After separa- 

 tion of the cord, the umbilicus becomes completely cicatrized by the 

 tenth or twelfth day. (Guy.) 



An exfoliation and renovation of the cuticle takes place over the 

 whole body soon after birth. According to Kolliker, the eyelashes, 

 and probably all the hairs of the bod}- and head, are thrown off and 

 replaced by others within the first year. 



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

 still enclosed 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 and fangs 

 of the tooth are formed subsequently by progressive elongation and 

 ossification of the tooth-pulp. The fully formed teeth emerge from the 

 gums in the following order: The central incisors in the seventh month 

 after birth ; the lateral incisors in the eighth month ; the anterior molars 

 at the end of the first year; the canines at a year and a half; and the 

 second molars at two years (Kolliker). The eruption of the teeth in 



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