360 



EXCRETION 



new cells, constantly increases the length of the nail. At the 

 same time the dermis just beneath the bed of the nail 

 forms new cells which add to its thickness. The matrix 



Fig, 166 — Sections of nails. A, median longitudinal section (X 4); <J) the fold at 

 the base of the nail; b, the nail; c, the bed of the nail. B, transverse section 

 ( X 4); a, lateral folds on each side of the nail; 6, the nail; c, bed of nail showing 

 papillte. C, portion of bed of nail (X 200); e, nail, formed of horny dermal scales; 

 d, deep layers of epidermis; c, papillse. 



may be compared to the hair papilla, and injury to hair or 

 nail will be repaired so long as the hair papilla or the nail 

 matrix is uninjured. The nail shows the following areas: 

 The part embedded in the dermal pocket is called the 



