TIII: ORGAVI Of UN OWM ;I-:UM EJ 3U7 



-kin, and ll.' tip .-f the tooth finally hreaks thron-h tin* epid.-rmal 

 c,. \d-iiiLr. The t...th then acquire- a Mill firmer at tachm-nt r 

 dermi> from tin- fact that, at the surface where the lower mar;.' 

 t lie il. Tit in.- occurs, salts of lime air deposited in the MIJ ertic ial layers 

 of the connective tiue (///-). and thus a kind of ronnei-t i\--t . 



ii in.-, tin- ct'iin'uhmi of t}te tooth, is produced 



Tin- finished tooth therefore is eonstrueted out of three calcified 

 tissut s, which arise from three fundaments. /'/< 



Fig. 170. -Longitudinal section through an older fundament of a dermal tooth of 



embryo. 

 e, Epidermis; t l , the deepest layer of epidermal cells, which are cubical; cA, mucous cells; 



/A', tin? ji.irt of the ilfiiiiis uhich is composed of connective-tissue lamellae ; Ik', superficial 



layer of the dennis ; .-... <ifiit;il papilla ; o, odontoblaato ; z6, deirane ; s, enamel ; sm, enamel- 



membrane. 



takes its oriyinfrom the odontoblast-l" <1> ,if<t! fxipilla (mesen- 



cJii/i/ii'). tin' < it<nD< I from the epithelial en ' (outer germ- 



ad the cementum from connective tissue 



IHI-HIIX f Direct ossification. The tini>hel t<H>tli has, moreover, 

 within it a cavity, which is tilled with a va>cular connect iv<- tissue 

 (/////;>), the remnant of the papilla. When the enamel-membrane 

 has fulfilled its office it peri-he-, f..r in the procos of secretion its 

 cells hecome shorter and >hoi-ter, and are finally reduced to f! 

 which are afterwards thrown oil'. 



In Selachians the formation of the teeth which occupy the edges 

 of the jaws and serve for the comminution of the food ditli-rs from 

 this simple process in one important point ; they take their origin, 

 not on the free surface of the mucous membrane, but in its 

 depths (fig. 171). Th< 'I tract of the oral mvcous membrane 



