STRUCTURE OF THE SKIN. 85 



This villous surface is observable on the skin, in almost 

 all quadrupeds. It is found in the soles of the feet only, in 

 birds and reptiles. In fishes and the inferior animals, its ex- 

 istence has not been satisfactorily ascertained. 



The corium may be observed in quadrupeds, birds, rep- 

 tiles and fishes. It is less distinct in the mollusca and crus- 

 tacea ; and in the animals ef the lower orders, it has not 

 been detected. 



From the experiments which have been made, to ascer- 

 tain the composition of the corium, it appears to consist 

 chiefly of gelatine. Hence it is that part which is employ- 

 ed in the manufacture of glue. In the thin, soft, flexible 

 hides, the gelatine does not possess the same degree of vis- 

 cidity, as in those of more rigid texture; and the glue ob- 

 tained from such, is proportionally weak. 



It has already been stated, that gelatine unites with tan- 

 nin, forming a substance which is insoluble in water. It 

 is to this combination that leather owes its peculiar proper- 

 ties. The skin is prepared for being converted into leather, 

 by maceration in water or lime-water, in order to remove 

 the cuticle and hairs. The tannin is obtained from oak-bark, 

 by infusion in water. The cleansed skin, now consisting 

 chiefly of gelatine, upon being placed in this infusion, 

 unites with the tannin. The strength of the leather de- 

 pends on the strength of the hides ; the more rigid these 

 are, the more tough and durable is the leather which they 

 furnish. 



4. Muscular web. -This is likewise termed Panniculus 

 carnosw. It varies greatly in its appearance according to 

 the motions which the skin and its appendices are destined 

 to perform. It consists of a layer of muscles, the extremi- 

 ties of whose fibres are inserted into the corium externally, 

 and adhere to the body internally in various directions. 

 This layer is very obvious, in the hedgehog and the poreu- 



