108 



THE ESSENTIALS OF HISTOLOGY 



into the papillae. Special branches are also distributed to the various 

 appendages of the skin, viz. the sweat-glands and hair-follicles, with 

 their sebaceous glands and little muscles, as well as to the little masses 

 of adipose tissue which may be found in the deeper parts of the cutis. 



The lymphatics originate near the surface in a network of vessels, 

 which is placed a little deeper than the blood- capillary network. They 

 receive branches from the papillae, and pass into larger vessels, which 

 are valved, and which run in the deeper or reticular part of the corium. 

 From these the lymph is carried away by still larger vessels, which 

 course in the subcutaneous tissue. 



The appendages of the skin are the nails, the hairs, with their 

 sebaceous glands and the sweat-glands. .They are all developed 

 as thickenings and downgrowths of the Malpighian laver of the epi- 

 dermis. 



FiG. 131. SECTION ACROSS THE ^TAIL, AND NAIL-BED. (100 diameters.) 



(Heitzmann.) 

 P, ridges with blood-vessels ; B, rete mucosum ; JV, nail. 



The nails are thickenings of the stratum lucidum of the epidermis, 

 which are developed over a specially modified portion of the corium, 

 which is known as the bed of the nail, the depression at the posterior 

 part of the nail-bed from which the root of the nail grows being 

 known as the nail-groove. The distal part of the nail forms the free 

 border, and is the thickest part of the body of the nail. The horny 

 substance of the nail (fig. 131, N) is composed of clear horny cells, 

 each containing the remains of a nucleus ; it rests immediately upon 

 a Malpighian layer (B) similar to that which is found in the epidermis 



