186 MR. TOYNBEE ON THE ORGANIZATION AND NUTRITION 



nutrition. Each of them is in contact, at its attached surface, with numerous and 

 large branches of the vascular system, and, with the exception of the teeth, each is 

 almost entirely composed of corpuscles or cells, which are of a somewhat circular 

 form, where they are near to the vascular chorion, and are compressed and flattened 

 where they are further removed from it. These tissues grow, by the addition to them, 

 at their point of attachment with the chorion, of new cells, and from the increase in 

 size of those already developed =*. 



The Epithelium is composed of corpuscles which are round where they are in con- 

 tact with the vascular chorion, and of others which are flat and in the state of scales 

 situated at its free surface. Immediately subjacent to the epithelium the chorion pre- 

 sents ramifications of blood-vessels which nourish it, and which have diff^erent cha- 

 racters in different portions of the mucous membrane, according to the various func- 

 tions which they have to perform. 



The chorion of the Integuments of the human subject, where it is subjacent to the 

 thin and delicate cuticle, presents a minute and intricate network of blood-vessels. 

 The arteries divide, subdivide, and form a network, from which the veins arise. The 

 vessels of the chorion, however, are difflerently arranged, where it is covered by thick 

 and dense cuticle. Thus, it is well known, that at the palms of the hands, the anterior 

 surface of the extremities of the fingers, the posterior part of the heel and at the 

 sole of the foot, the thick Epidermis forming corns, &c., the arteries of the chorion are 

 observed to terminate in numerous dilated loops, a disposition which bears a close 

 analogy to certain synovial vessels. 



The vessels of the chorion have the function, not only of secreting the perspira- 

 tion, but of developing and nourishing the ducts through which the latter fluid is 

 excreted -f-. 



In parts where the Epidermis undergoes a still greater degree of condensation, and 

 is found in larger masses than in parts already alluded to, the vascular system of the 

 chorion presents still greater dilatations, and more complicated arrangements. Such 

 parts are the nails and claws, hoofs, hair and bristles, feathers and horn. 



The Nails. — Where the nails are in cohesion with the vascular chorion, they are 

 more or less soft; and when portions of them at this part are examined by the micro- 

 scope, they are seen to consist of corpuscles somewhat compressed and connected to- 



* In the first edition of his Elements of Physiology, page 384, Muller enters upon an examination of the 

 mode of growth " of unorganized non-vascular parts." These he divides into three classes: — I. The homy 

 tissues ; 2. The teeth ; 3. The crystalline lens. In the second edition, p. 416, having omitted the word unorgan- 

 ized, he adds, " These parts, however, though not vascular, and though formed in the manner which we have 

 described, have nevertheless a definite structure or organization, and afford confirmation of our previous remarks, 

 that the vessels are merely destined to pour out the materials for nutrition, and that the formation of the ele- 

 mentary parts of each tissue takes place in the matter effused independently of any action of the vessels." 



t The waUs of the perspiratory ducts of the cuticle appear to me to be formed of a single filament (itself 

 composed of corpuscles) spirally arranged, having thus an analogy with the spiral ducts of plants. 



