STRUCTURE OF SKIN. 717 



be cut with the curved scissors from any part that affords them ; 

 and these must be torn -asunder with needles under the Simple 

 Microscope, until the fibres are separated to a degree sufficient to 

 enable them to be examined to advantage under a higher magnify- 

 ing power. The difference between the 'White ' and the 'Yellow' 

 components of Connective tissue is at once made apparent by the 

 effect of Acetic acid; whilst the 'Connective-tissue-corpuscles' 

 are best distinguished by the Staining-process (§ 145), especially in 

 the early stage of the formation of these tissues (Fig. 376). 



560. Skin, Mucous, and Serous Membranes. — The Skin which 

 forms the external envelope of the body, is divisible into two prin- 

 cipal layers ; the Cutis vera or 'True Skin,' which usually makes 

 up by far the larger part of its thickness, and the 'Cuticle,' 

 'Scarf-skin,' or Epidermis, which covers it. At the Mouth, 

 Nostrils, and the other orifices of the open cavities and canals of 

 the body, the Skin passes into the membrane that lines these, 

 which is distinguished as the Mucous membrane, from the peculiar 

 glairy secretion of Mucus by which its surface is protected. But 

 those great closed cavities of the body, which surround the Heart, 

 Lungs, Intestines, &c, are lined by membranes of a different kind ; 

 which, as they secrete only a thin serous fluid from their surfaces, 

 are known as Serous membranes. Both Mucous and Serous mem- 

 branes consist, like the Skin, of a proper membranous basis, and 

 of a thin cuticular layer, which, as it differs in many points from 

 the epidermis, is distinguished as the Epithelium (§ 563). — The 

 substance of the 'True Skin' and of the 'Mucous' and 'Serous' 

 membranes is principally composed of the Fibrous tissues last de- 

 scribed ; but the Skin and the Mucous membranes are very copiously 

 supplied with Blood-vessels and with Grlandulse of various kinds ; 

 and in the Skin we also find abundance of Nerves and Lymphatic 

 vessels, as well as, in some parts, of Hair-follicles. The general 

 appearance ordinarily presented by a thin vertical section of the 

 Skin of a part furnished with numerous Sensory papillce (§ 572), 

 is shown in Fig. 378 ; where we see in the deeper layers of the 

 Cutis vera little clumps of Fat-cells, /, and the Perspiratory 

 gland ulse d, d, whose Ducts, e, e, pass upwards; whilst on its 

 surface we distinguish the vascular Papilla?, p, supplied with 

 loops of Blood-vessels from the trunk, g, and a tactile Papilla, t, 

 with its Nerve-twig. The spaces between the papilla; are filled-up 

 by the soft Malpighian layer, m, of the Epidermis, a, in which its 

 colouring matter is chiefly contained ; whilst this is covered by the 

 horny layer, h, which is traversed by the spirally-twisted continua- 

 tions of the perspiratory ducts, opening at s, upon the surface, 

 which presents alternating depressions, a, and elevations, b. — The 

 distribution of the Blood-vessels in the Skin and Mucous mem- 

 branes, which is one of the most interesting features in their 

 structure, and which is intimately connected with their several 

 functions, will come under our notice hereafter (Figs. 394, 397, 



