108 



material which they contained has been recently removed, or still re- 

 mains within them in the form of whitish, globular masses. The situ- 

 ation of these lacunae, where the openings themselves are not apparent, 

 can be distinguished by the plexus of capillaries in their vicinity, in 

 the areolae of which their openings are situated. 



The Growth of the Nails. 



The growth of the nails is effected exclusively by the continued se- 

 cretion of horny matter at their roots, the particles of which, while in 

 the act of being deposited, force forwards all those which had been 

 deposited previously. Hence the nails grow only in one direction, 

 namely, from behind forwards. This fact is evident from the well- 

 known experiment of making two marks with lunar caustic near the 

 root of a nail, and observing their progress towards its free border, 

 when they will be seen to preserve always the same distance from one 

 another, on whatever part of the nail they may be situated. Now 

 from this fact it is obvious that the proper material of the nail is se- 

 creted from the vessels situated the most posteriorly of the three sets 

 just described, that is, from the convoluted capillaries situated be- 

 neath the lunula, the position of these vessels being such as to render 

 it impossible that a substance constantly separated from the blood 

 within them, and deposited on their exterior, can do otherwise than 

 continually protrude forwards the whole of a nail at the same time. 

 For the horny matter proceeding, doubtless in a fluid state, from these 

 convolutions, is, on quitting them, so compressed between the fold of 

 skin which overhangs the root of the nail, the posterior part of the 

 matrix itself, and the fibrous groove connecting these, as to be pre- 

 vented passing in any direction excepting forwards, and even this it 

 cannot do without displacing the whole of the nail at the same time, 

 as before shown. Hence in this manner a direction is given to the 

 nail forwards, and the other convolutions adding at the same instant 

 the horny matter secreted from them, this part of the nail is com- 

 pleted, and its thickness determined, which therefore does not increase 

 afterwards. This part of the nail being now formed, has to pass 

 over the other portions of the matrix, from which it receives the cuti- 

 cle requisite to connect its inferior surface with the cuticle at the end 

 of the finger. In the vertical section of nail represented by PI. 22, 

 fig. 2, the cuticle on the inferior surface of the nail is seen to extend 

 no further back than the lunula. Also, in the transverse section 

 through the nail, a little behind its free edge, represented by PI. 22, 



