THE NAILS 



1295 



of the nail and is deepest in the centre of the root, becomes shallower toward the 

 lateral margins, and finally disappears entirely toward the free border of the 

 nail (figs. 1055, 1056). 



The dorsal free exposed surface of the nail is formed by a hardened, thickened, horny layer of 

 epithehum corresponding to the deeper parts of the stratum corneum (or the stratum lucidum) 

 of the skin, the stratum corneum unguis (fig. 1056). It is convex from side to side (especially 

 on the fifth finger), and also in some cases longitudinally. It presents a number of more or less 

 well-marked fine longitudinal ridges. The stratum corneum forms the principal thickness of 

 the nail. It is thicker and more solid on the toes than on the fingers. The portion of the 

 nail which projects beyond the skin of the fingers and toes is greyish-white in colour. Unless 

 broken or cut, it curves ventrally upon the ball of the finger or toe and tends to become long and 

 claw-like. It may attain a length of 3 or more centimetres. 



The concave volar or plantar surface of the nail is softer and is formed of a layer of epithelial 

 cells which corresponds to the stratum germinativum (Malpgihii) of the skin and is known as 

 the stratum germinativum unguis (fig. 1056). Because of the transparency of both layers of 

 the nail the blood in the underlying matrix is seen through the body of the nail and gives to it a 



Fig. 1056. — Cross-section Through the Nail and Tip of the Ring Finger. (X 4). 



(From Toldt's Atlas.) 



Corpus unguis- 



Cristse matricis unguis y^ / /^ 

 Vallum unguis 





Sulcus matricis 

 unguis 



Phalanx III 



Periosteum 



Retinacula cutis 



Cristas cutis 

 Volar surface of finger 



Stratum corneum unguis 

 Stratum germinativum 

 Matrix unguis 



Margo lateralis 

 unguis 



pinkish colour; but toward the root of the nail there is a semilunar area convex distally, the 

 lunula, which is less transparent and opaque whitish in color (fig. 1053). The lunula is vari- 

 ously developed in different individuals. It is largest on the thumb andis often absant on the 

 little finger. It is also smaller on the toes than on the fingers. 



The stratum corneum unguis consist of thin, flattened, transparent, horny scales with shrunken 

 nuclei. These cells are intimately joined together in thin layers. The stratum germina- 

 tivum unguis is formed of cells continuous with and resembling those of the corresponding 

 layer of the epidermis. Air may occur between the cells as with the hair. The cells of the root 

 are not yet cornified or dried out. 



The stratum germinativum unguis rests upon the corium, which here forms the so-called 

 nail bed [matrix unguis]. ^ This is made up of a dense feltwork of connective tissue fibres 

 without fat. It is highly vascular and sensitive and the vertically arranged bundles bind the 

 nails tightly to the periosteum of the terminal phalanges. The papillee of the matrix beneath the 

 body of the nail are arranged in strongly marked longitudinal ridges, the cristse matricis unguis. 

 The cristse and papillae of the matrix fit into corresponding depressions on the deep smiace of 

 the stratum germinativum unguis. 



The cristse of the matrix are small and low proximally and become larger and fewer distally. 

 Those toward the lateral borders are somewhat oblique. The papillse of the root are not in rows 

 but are irregularly arranged and disappear entirely near the distal border of the lunula. Toward 

 the free border of the nail the papillse become large and change in character to that of the adja- 

 cent skin. 



The best developed nails are those of the thumbs and great toes, the least developed, those 

 of the fifth digits which on the toes are often represented only by a horny tubercle. 



Blood-supply of the nails. — The arteries are numerous in the matrix beneath the body of the 

 nail but fewer beneath the root. They pass from the deep parts of the nail bed toward the sur- 

 face, running in the main longitudinally and sending anastomosing branches to the papillse. 



The nerves beneath the nail are abundant and terminate in free sensory endings and in special 

 end organs of several sorts. 



^ The term nail bed is applied by some anatomists to that part of the corium beneath the 

 body of the nail, the term matrix being reserved for the corium beneath the lunula and root. 



