STRUCTURE OF THE DERMA. 469 



rtratum, on the other hand, is fine in texture, reddish in colour, soft, 

 raised into minute papillae, and highly vascular and sensitive. These dif- 

 ferences in structure have given rise to a division of the derma into the 

 deep stratum, or corium^ and the superficial, or papillary layer. 



In the Corium the areolo-fibrous tissue is collected into fasciculi, which 

 are small and closely interwoven in the superficial strata, large and coarse 

 in the deep strata ; in the latter forming an areolar network with large 

 areolae, which are occupied by adipose tissue. These areolse are the 

 channels by which the branches of vessels and nerves find a safe passage 

 to the papillary layer, in which and in the superficial strata of the corium 

 they are principally distributed. The yellow elastic tissue is found chiefly 

 in the superficial strata, the red contractile tissue in the deep. It is to the 

 latter that the nipples and scrotum owe their contractile powers, and the 

 general surface of the skin the contraction which is known by the name 

 of cutis anserina. The corium presents some variety in thickness in dif- 

 ferent parts of the body. Thus in the more exposed regions, as the back, 

 the outer sides of the limbs, the palms, and the soles, it is remarkable for 

 its thickness ; while on protected parts it is comparatively thin. On the 

 eyelids, the penis, and the scrotum, it is peculiarly delicate. It is con- 

 nected by its under surface with the common superficial fascia of the body. 



The Papillary layer of the derma is raised in the form of conical promi- 

 nences or papillae. On the general surface of the body the papillaB are 

 short and exceedingly minute ; ,but in other situa- 

 tions, as the palmar surface of the hands and fingers, 

 and the plantar surface of the feet and toes, they 

 are long and of large size. They also differ in 

 arrangement ; for, on the general surface they are 

 distributed at equal distances and without order; 

 whereas, on the palms and soles, and on the corre- 

 sponding surfaces of the fingers and toes, they are 

 collected into little square clumps containing from 

 ten to twenty papillaB ; and these little clumps are 

 disposed in parallel rows. It is this arrangement 

 in rows that gives rise to the characteristic parallel 

 ridges and furrows which are met with on the hands 

 and feet. The papillaB in these little square clumps 

 are for the most part uniform in size and length, but every here and there 

 one papilla may be observed which is longer than the rest. The largest 



* Anatomy of a portion of skin taken from the palm of the hand. 1. The papillary 

 layer, in which the longitudinal furrows (2) marking the arrangement of the papillae 

 into ridges is shown. Each ridge is moreover divided by transverse furrows (3) into 

 small quadrangular clumps. The quadrangular clumps consist of a tuft of minute 

 conical papillae, of which one or two are frequently longer and larger than the rest. In 

 this figure the long papillae are alone seen, the rest being too numerous to introduce into 

 a wood-engraving. 4. The rete mucosum raised from the papillary layer and turned 

 back; the under surface of this stratum presents an accurate impression of the papillary 

 layer; on which are seen longitudinal ridges corresponding with the longitudinal fur 

 rows, transverse ridges corresponding with the transverse furrows, and quadrangula- 

 depressions corresponding with the quadrangular clumps of papillae. Moreover, wher- 

 ever one of the long papilla? exists, a distinct conical sheath will be found in the rele 

 mucosum 5, 5. Perspiratory ducts drawn out straight by the separation of the rete mu- 

 cosum from the papillary layer; the point at which each perspiratory duct issues from 

 the papillary layer, and pierces the rete mucosum, is the middle of the transverse furrow 

 between the quadrangular masses. 



40 



