774: 



DEVELOPMENT OF THE NERVOUS SYSTEM. 



Fig. 286. 



direction of the head and upper part of the body. Subsequently the 

 spinal column becomes straighter and loses its twisted form. At the 



same time the pelvis and the muscular parts 

 seated upon it grow so much faster than the 

 sacrum and coccyx, that the latter become 

 concealed under the adjoining soft parts, 

 and the rudimentary tail disappears. 



The integument of the embryo is at first 

 thin, vascular, and transparent. It after- 

 ward becomes thicker, more opaque, and 

 whitish in color. Even at birth, however, 

 it is considerably more vascular than in the 

 adult condition, and its ruddy color, due to 

 its transparency and the abundance of its 

 capillary bloodvessels, is strongly marked. 

 The hairs begin to appear about the middle 

 of intra-uterine life; showing themselves 

 first upon the eyebrows, afterward upon the 

 scalp, trunk and extremities. The nails are 

 in process of formation from the third to 

 the fifth month ; and, according to Kolliker, 



are covered with a layer of epidermis until after the latter period. The 

 sebaceous matter of the cutaneous glandules accumulates upon the skin 

 after the sixth month, and forms a whitish, semi-solid, oleaginous layer, 

 the vernix caxeosa, which is most abundant in the flexures of the joints, 

 between the folds of the integument, behind the ears, and upon the scalp. 



HUMAN EMBRYO, about one 

 month old. Showing the large 

 Bize of the head and upper parts 

 of the body; the twisted form of 

 the spinal column ; the rudiment- 

 ary condition of the upper and 

 lower extremities ; and the rudi- 

 mentary tail at the end of the 

 spinal column. 



