540 ELEMENTARY PHYSIOLOGY 



constitutes the mucous membrane lining the alimentary 

 canal, and also occurs in the so-called "glandular" tissue. 

 The structure of these, as also of muscle and nerve and 

 bone, has been already described, so that we may confine 

 our attention here to the other principal tissues^ 

 epithelial tissues, the connective tissues and cartilage. 



6. The Epidermis. — A good example of this tissue is 

 to be found in the skin, which, as we have seen (Lesson 

 v.), consists of the superficial epidermis which is non- 

 vascular and epithelial in nature, and of the deep dermis, 

 which is vascular, and is indeed chiefly composed of 

 connective tissue carrying blood-vessels and nerves. And 

 in all the mucous membranes there is a similar superficial 

 epithelial layer, which is here simply called epitheliem, 

 and a deep layer, which similarly consists of connective 

 tissue carrying blood-vessels and nerves and may also be 

 spoken of as dermis. 



If a piece of fresh skin is macerated for some time in 

 water, it is easy to strip off the epidermis from the 

 dermis. 



The outer part of the epidermis which has been de- 

 tached by maceration will be found to be tolerably dense 

 and coherent, while its deep or inner substance is soft and 

 almost gelatinous. Moreover, this softer substance fills up 

 all the irregularities of the surface of the dermis to which 

 it adheres, and hence, where the dermis is raised up into 

 papillae, the deep or under surface of the epidermis 

 presents innumerable depressions into which the papillfe 

 fit, giving it an irregular appearance, somewhat like a net- 

 work. Hence it used not unfrequently to be called the 

 network of Malpighi (rete Malpighii), after a great 

 Italian anatomist of the seventeenth century, who first 

 properly described it. On the other hand, its soft and 

 gelatinous character 'led to its being called mucous layer 

 {stratum Tnucosum). Chemical analysis shows that the 

 firm outer layer of the epidermis differs irvm the deep 

 soft part by containing a great deal of horny matter. 



