OF THE SKIN. 135 



general sketch of the development in the foetus, of the cutis in the 

 broadest sense of the term. It consists at first of cells, which though 

 not in man, yet in animals (the Frog, for instance) may be easily traced 

 back to the earliest formative cells of the embryo. A considerable pro- 

 portion of these cells are changed into connective tissue, becoming fusi- 

 form, coalescing, and eventually being converted into bundles of fibrils; 

 a process which appears to occur first in the fascia superficialis, the sub- 

 cutaneous connective tissue, then in the pars reticularis of the corium, 

 and finally in the papillary layer. Another portion of the cells are 

 converted into vessels and nerves, as can be seen even in man, and very 

 beautifully in the Batrachia (see my Memoir in the "Annales des 

 Sciences Naturelles," 1846) ; while a third, growing and developing fat 

 in its interior, becomes elastic fibres and fat-cells (vide supra, 23). 

 The first foundations of all these parts having been laid, they continue to 

 increase in a manner which is not yet exactly made out. The cutis ob- 

 viously grows from within outwards (so that the papillae arise and are 

 developed last of all), partly by the growth of its primitive elements, 

 partly at the expense of cells, which are perhaps mostly of new forma- 

 tion, and do not proceed from the original formative cells. The panni- 

 culus adiposus also increases, partly by the increase of the cells of which 

 it at first consists, partly by the subsequent development of others, as 

 well as of connective tissue and vessels. In this manner, the skin grows 

 for a long time after birth. In children below seven years of age, for 

 example, the cutis is, according to Krause, only half as thick as in the 

 adult, until at last, though at a time which is yet undetermined, the new 

 development of cells ceases, as at a later period, perhaps, does the ex- 

 tension of those elements, cells, fibres, &c., which are already formed. 

 The fat-cells of adults, in which the process of growth is especially ob- 

 vious, according to Harting, are in the orbit twice, in the palm three 

 times as large as in the new-born infant ; whence it results that they in- 

 crease in size in proportion to the parts of the body to which they belong. 



In embryos of two months the skin is 0'006-0*01 of a line thick, 

 and wholly composed of cells. At the third month it is about 0-06 of 

 a line, and already presents tolerably distinct connective tissue. In the 

 fourth month the first lobules of fat appear, and the ridges of the hand 

 and sole of the foot. From the seventh month onwards the panniculus 

 adiposus is rapidly developed, and at birth it is relatively thicker than 

 in the adult. 



39. Physiological Remarks. If we attempt to harmonise the ana- 

 tomical data here brought together, with the phenomena of sensation 

 exhibited by the skin, we meet with considerable difficulties. The more 

 intimate anatomy of the skin, as it is here detailed, fails to demonstrate 

 nerves in all the papillae, or even in the majority of them ; and yet ex- 



