Chap, xxxiv.] THE SKIN. 289 



by which the nail-matrix passes into the surrounding 

 skin. 



394. The substance of the nail is made up of a 

 large number of strata of homogeneous horny scales 

 the nail-cells each with a staff-shaped remnant of a 

 nucleus. 



The coriutn of the nail-bed is highly vascular ; it 

 is firmly fixed by stiff bands of fibrous tissue on the 

 subjacent periosteum ; it is covered with a stratum 

 Malpighii of the usual description, except that the 

 stratum granulosum is absent in the nail- matrix, but 

 is present in a rudimentary state in the rest of the 

 nail-bed. The nail itself represents the stratum 

 lucidum, of course of exaggerated thickness, situated 

 over the stratum Malpighii of the nail-bed. There 

 is no stratum corneum over the nail. 



The stratum Malpighii and corium of the nail-bed 

 are placed into permanent minute folds, and the nail 

 possesses on its lower surface corresponding linear 

 indentations. 



395. In the foetal nail-bed the stratum Malpighii 

 is covered with the usual stratum lucidum and stratum 

 corneum, but the former is the larger; by a rapid 

 multiplication of the cells of the stratum Malpighii, 

 and a conversion of its superficial cells into the scales 

 of the stratum lucidum, the foetal nail is produced. 

 At this early stage the nail is covered by stratum 

 corneum. By the end of the fifth month the margin 

 breaks through this stratum corneum, and by the 

 seventh month the greater part has become clear 

 of it. 



396. The blood-vessels of the skin. The 

 blood-vessels are arranged in different systems for the 

 different parts of the skin (Tomsa) : 



(a) There is, first, the vascular system of the 

 adipose tissue, differing in no way from the dis- 

 tribution of blood-vessels in fat tissue of other places. 



