INTRODUCTORY. 



17 



are modified mucous memhrane. The skin consists of 

 exactly the same component elements as other membranes, 

 but they are generally more complex. It is in many 

 parts continuous with the larger mucous membrane, and 

 all over its surface presents openings leading into glands. 

 It presents modifications under the form of hair and hoof. 

 It consists of two parts separated by basement membrane, 

 dermis and ejiidermis. The dermis corresponds to the 

 corium of mucous membrane, and consists of a more or 

 less thick layer of reticulated yellow elastic and white 

 fibres, containing in their meshes vessels and nerves. It 

 presents two layers, the reticulated and papillated. The 

 reticulated layer internally situated, its deep-seated surface 

 is continuous with the subcutaneous areolar tissue, its 

 superficial with the papillated layer, which is externally 

 raised into a number of finger-like prominences (covered 

 with basement membrane), on to which the epidermis is 

 moulded. The subcutaneous areolar tissue varies in its 

 density in different parts of the body, being in some places 

 very loose, as in the intermaxillary space, on the chest, &c. 

 These parts are most liable to dropsical collections and 

 most readily admit insertion of setons. It contains col- 

 lections of fat, the terminations of the hair-follicles and of 

 the sudoriparous glands. Portions of these also, and the 

 sebaceous glands, are embedded in the dermis. The 

 epidermis consists of epithelial cells moulded upon the 

 external surface of the dermis ; the most deep-seated are 

 spheroidal and contain pigment-granules, forming the rete 

 mucosum. The superficial layers become hard, dry, and 

 scaly ; as they are subjected to external influences, they are 

 gradually worn away. 



Hairs are produced from depressions on the surface of 

 the skin termed hair-follicles. These are filled with 

 spheroidal epithelium, and into each of them open gene- 

 rally the ducts of two sebaceous glands. At its deep- 

 seated extremity, where it forms a cul-de-sac, each follicle 

 presents a papilla from which the hair is produced. The 

 hair is the epithelium of the papilla (which is of the same 

 nature as the dermis). It consists of a hulh, apex, and 

 shaft. The hulb immediately surmounts the papilla, and 

 is the largest portion of the hair, consisting of the softest 

 and most recently formed spheroidal cells. The shaft is 

 the cylindrical portion which runs outwards, emerges from 



