1076 THE SKIN 



grades leading to complete keratinisation, their career is ended and they are cast 

 off from the t^tratum corneum. Xo vessels exist in any ])art of the epiderm, Imt 

 nerve-tibrils are said to penetrate as far as the stratum Malpighii. 



In the more recent methods of skin-grafting the surgeon takes a jjlane which 

 usually includes all the layers of the epidermis, and even the extreme tips of the 

 papilla? of the derm (as shown by the minute bleeding points left on the surface 

 from Avhich the graft has been cut). The absence of the deeper and more highly 

 vitalised epidermic cells in the pellicle separated by a blister is probably responsible 

 for the almost uniform failure of transplantation of this material. 



VESSELS OF THE SKIN 



The arteries of the skin form a network in the subcutaneous tissue, and from 

 this arise branches which })ass outwards into the derm, and, after supplying twigs 

 to the glands and hair-bull)s, unite into a second network beneath the papillae, 

 supplying these latter with tine arterioles, which finally break up into a capillary 

 plexus. The veins commencing within the papillae form a subpapillary network 

 which ends in the subcutaneous veins. The hnnphatics have a like arrangement. 



Nerves. — The skin is richly supplied with nerves, but in varying degrees in 

 different regions. Everywhere the nerves form plexuses in the derm, the network 

 becoming finer as it approaches the epiderm, forming a rich subepithelial network 

 immediately beneath the stratum basilare. From this, delicate tiljrils have been 

 traced outwards as far as the stratum Malpighii, where they terminate. The integu- 

 mentary nerves end in three different Avays — some in subcutaneous bodies, the cor- 

 puscles of Pacini or Vater; others in dermic structures, the corpuscles of ]Meissner 

 and Krause; and a third, or epidermic set, are believed to terminate in minute 

 bulbs. 



The corpuscles of Pacini may be found attached, like berries, to the nerve- 

 stems lying in the subcutaneous tissue in various parts of the surface, but most 

 abundantly on the digital nerves. They are not confined to the cutaneous nerves, 

 but are seen also upon mixed nerves, such as the intercostal; upon articular, peri- 

 osteal, and other nerves; and even on sympathetic filaments, such as those of the 

 mesentery. They are of oval form, and range in size from oV to i of an inch 

 (1 to 5 mm. ). Structurally, they consist of a connective-tissue envelope derived from 

 the perineurium and a series of thirty to sixty concentric fil^rous tunics each, lined on 

 both sides by endothelium; within is a central structureless core. The nerve-tibre 

 pierces one of the poles of the corpuscle and reaches the central core, Avhere it loses 

 its myelin and subdivides into delicate ramilications, which end in small bulbous 

 enlargements. Each liody is supplied by a set of vessels that form plexuses and 

 loops in the layers of the capsule. 



The tactile corpuscles of Meissner are of smaller size and more limited dis- 

 tribution than the Pacinian bodies. They belong almost entirely to the hands and 

 feet, but may lie found also over the radial side of the forearm, in the mamnnlla 

 and the red l)order of the lips, as well as in the free border of the conjunctiva and 

 in the mucous meml)rane of the tip of the tongue. They are particularly numerous 

 over the pulp of the terminal phalanges, wdiere the sense of touch is most acute. 

 They lie within certain of the papillae, which they occupy to the exclusion of ves- 

 sels, and appear as solid, olive-shaped bodies about -^ of an inch in length (tV of 

 a mm. ) placed with their long axes at right angles to the surface. Each is Joined 

 at its deeper extremity by one, two, or more nerves. In structure the corpuscle 

 consists of a connective-tissue capsule, like that of the Pacinian body, derived from 

 the perineurium; within this is a solid cellular structure, in wliich the nerve cylin- 

 der, deprived of its myelin, l)reaks up into filaments, to end either in bulbous 

 or discoid enlargements. 



The spheroidal end-bulbs of Krause, found in the conjunctiva and mucous 

 membrane, and in a modified form in the prepuce and glans penis and clitoridis, 

 bear some resemblance to the tactile corpuscles and to the central core of the Paci- 

 nian bodies. They consist of a connective-tissue capsule enclosing a cellular 

 structure in which the nerve terminates. 



