RETE MUCOSUM. 465 



these situations are separated from each other by longitudinal fur- 

 rows, and are divided by transverse furrows into small quadrilateral 

 rounded masses. These quadrilateral masses are each composed 

 of a considerable number of minute papillae, which are conical in 

 form and variable in* length, one or two of the papillae in each mass 

 being generally longer than the rest. In the middle of the trans- 

 verse furrow, between the papilla?, is the opening for the perspira- 

 tory duct. 



The papilla? beneath the nail have a peculiar form and arrange- 

 ment. At the root of the nail they are numerous, but small and 

 very vascular ; opposite to the part of the nail called lunula, they 

 are scarcely raised above the surface, and less vascular; but beyond 

 this point they form lengthened vascular plicae, which afford a large 

 surface of secretion. These lengthened papillas deposit the horny 

 secretion in longitudinal lamellas, which give to the nail the ribbed 

 appearance which it presents upon its surface. 



Vessels and Nerves. The papillae are abundantly supplied with 

 vessels and nerves ; the former to enable them 

 to perform the office of secretion in the pro- Fig. 143.* 



duction of the cuticle, the latter to give them 

 the sensibility necessary to an organ of touch. 



The Rete mucosum is the soft medium w r hich 

 is situated between the papillary surface of 

 the cutis and cuticle ; after a careful macera- 

 tion it may be separated as a distinct layer, 

 particularly in the negro, where it is firmer 

 than in the European, and contains the colour- 

 ing matter of the skin. 



The name rete mucosum, given to it by 

 Malpighi, conveys a very inaccurate notion 

 of its structure; for it is neither a network, 

 nor is it mucous. It is thin upon the general surface of the body ; 

 but is thicker in the palm of the hand and sole of the foot, and pre- 

 sents a close correspondence with the thickness of the cuticle. 

 Examined with the microscope, it is seen to be moulded accurately 

 upon the papillae, being thick in the spaces between these, and thin 



* Anatomy of a portion of skin taken from the palm of the hand. 1, 1. The papil- 

 lary layer, in which the longitudinal furrows (2) marking the arrangements of the 

 papillse into ridges is shown. Each ridge is moreover divided by transverse furrows 

 (3) into small quadrangular masses. The quadrangular masses 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 papilla? are alone seen, the rest being too numerous to 

 introduce into a wood-engraving. 4, 4. The rete mucosum raised from the papillary 

 layer and turned back; the under surface of this stratum presents an accurate impres- 

 sion of the papillary layer ; on which are seen longitudinal ridges corresponding with 

 the longitudinal furrows, transverse ridges corresponding with the transverse furrows, 

 and quadrangular depressions corresponding with the quadrangular masses of papillee. 

 Moreover, wherever one of the long papilla? exists, a distinct conical sheath will be 

 found in the rete mucosum. 5, 5. Perspiratory ducts drawn out straight by the sepa- 

 ration of the rete mucosum from the papillary layer ; the point at which each perspi- 

 ratory duct issues from the papillary layer, and pierces the rete mucosum, is the middle 

 of the transverse furrow between the quadrangular masses. 



59 



