OF THE NAILS. L67 



be reckoned as proper nail substance) ; it increases by the 

 extension of its elements and by the addition of new ones at 

 its edges ; but it remains even to the end of the fifth month, 

 hidden under the horny layer of the epidermis, until finally 

 it becomes free, and in the seventh month, even begins to grow 

 longitudinally, so that at this period, except in its greater soft- 

 ness and its smaller dimensions, it presents no essential differ- 

 ence from the perfect nail. With regard to the bed of the 

 nail, its ridges are already indicated at the end of the fourth 

 month, and in the fifth they are well marked, 0*02 — 0-024'" 

 deep, 0-004 — 0-005'" broad, and 0008 — 0-014'" distant ; these 

 measurements also indicate the breadth of the laminae of the 

 stratum Malpighli. At the sixth month they are somewhat 

 larger and further apart. 



In the new-born infant, the whole nail is 0-3 — 0-34" thick ; 

 0-16'" being proper nail substance, 0*14 — 0-18'" stratum Mal- 

 pighii. Its elements are still almost identical with those at the 

 sixth month, and they appear with tolerable distinctness in the 

 nail proper without any reagents, as elongated polygonal nu- 

 cleated plates 002 — 0-028'", as Schwann has already partly re- 

 marked. The free edge, projecting far forwards, which is 

 presented in all nails, is worthy of remark. It is considerably 

 thinner and narrower than the body, and is separated from 

 it by a semilunar line ; it is rounded anteriorly, as much as 

 2'" long, and is plainly nothing but the nail of an earlier 

 period which has been thrust forward by the longitudinal 

 growth of the nail in the course of its development. In 

 fact it nearly corresponds in size with a nail of the sixth 

 month. 



Soon after birth the long free edge of the nail of the new- 

 born infant is cast off, at least once (according to Weber many 

 times), in all probability in consequence of external mechanical 

 violence, which it is unable, owing to its delicacy, to resist. 

 In the sixth and seventh months after birth, I find that 

 the nails which the child brought into the world, are com- 

 pletely replaced by new ones, and in the second and third 

 years the nail-plates are not distinguishable from those of the 

 adult, whence it follows that the nail increases in thickness, 

 less in consequence of any enlargement of its elements, than by 

 the addition of new ones to its edges and under-surface. 



