UN TER GERM-LAYER. 



amniot ic tin:, ike it mil.!. I. Finally these, as well as 



of the ii. Mvallou.-d i.y t he embryo 



t lit- amniotic tluid, ami lhu> I..-.-..MI.- a < of the U10C- 



acciimulatt .1 in tin- ii ' 



Tin* epidi-rmi bet only on.- cmp 



adult <T of ili- integument : th nd mop- \ iu part 



tin- /'////'/ OrC -duced l.y t|i> n. I :..- 



Bfl place here as in the cuso of the other membranes and organs 

 he body. The epithelial layers derit< th* primary </ 



1 1 to dose relation*/' the mesenchyme t since they 



a i- .|uire from the latter a c<> ^erves for 



their mechanical support and nutrition. .Ju-t a -ir germ- 



layer unites with the Intermediate layer to form the mucous mem- 

 of the alii: -inal. as th< ej.ith'-liu: 



with the adjacent connective substance to form the mem- 

 Kranous labyrinth, and as the epitlielial op le with th' 



and scli-ra to form the eyeball, so here aU> t In- fj.id.-i mi- nnit.-s \\itli 

 the corium to const it nto the inte^nim-nt. 



During the iirst months tin- corium forms in Man a layer of 



y packed. >j>indle-shaped cells, and is delimited from the 

 epidermis by a delicate, structureless, smo< "d. Km- 



ni'-mlirane (liasem-nt minlraiu). surli as exists perin 



of tlie lower Vertebrates. In the third month it is .1 

 rntiated into the corium proper :i;>d the looser subcutaneous tissue, 

 in which then- are >oon developed duM.-r> of i N. From 



middle of preirn.-nii-y onward t ho latter so increase in number 

 the xilicutam ou> ii>sue soon becomes a layer ot tini: tin- 



whole body. At this time the smooth contour between epidermis 

 and corium is 1 M . o\\ ing to the development on 



r of small papilla-, which grow into the mucous layer and 

 produce the corpus papillate of the \ be papilla* serve pa 



for the reception of loops of capillary 1 >lood-vessels, and thus effect 

 a better nutrition of the mucous layer; in part they nv ive the 

 termination- of tactile nerves (tactile hus are 



divided into vascular papilla- and ner\oiis papilhe. 



The >kin of Vertebrates attains a higher degree of development in 

 consequence of processes similar to those described -.te^inal 



(anal. The epidermis increases its surface outward by the formation 

 off< <>;i9. Because the evaginated and 



inva^'inated parts at the Same tiim- alter in many ways t' 

 'gical peculiai iti. .>, there arises a large number of organs of 



