62 .l.UA'A'/r.LV MrSKUM aUIDE LEAFLETS 



the size of the yoiin^ skull, their ant('r()-])()st('ii()r incasurcincnt being a 

 little j»;reater than that of theii- successors, the premolars, and occuj)y the 

 entile s|)ace in llie skull wliicli will finall\- accommodate the whole giind- 

 in^i; set, so that ///. is crowded far hack, I)ej2;inninjj; its (leveloj)nient in the 

 alveolar cavity directly below the eye socket, as shown in fijjjure 38A, a 

 colt two days old. This discicpancy, however, is nicel}' adjusted. As 

 fast as the increasing!; size of the skull will jxMinit, the teeth are crowded 

 forwai'd with a horizontal movement, makin«2; room at the back for the 

 development of the molars, each one resigning its birth-place below the 

 eye, and moving forward to make room for the next one to fall in line, the 

 o])eration being about the same in the lower set as in the upi)er teeth. 



The incisors also encroach upon the i-egion of the very small d. c. -f 

 particulai'ly d i. ■(, which begins its development well back of the d. c. — 

 (Fig. 38.4 j. As the jaw grows, d. i. jt passes forwai-d and assumes its final 

 position in front of the d. c. -^. 



At ekn-en months (Fig. 38B) the deciduous teeth are all in use and 

 most of them considerably worn. m. -, which is due to erupt within 

 about a month, has increased wonderfully in length and has moved for- 

 w^ard, giving up the place under the eye to m. ~, which has already at- 

 tained considerable size, and has advanced somewhat in its forward 

 movement. Between the roots of d. m. -, which are flattened and widely 

 spread apart, thus making room for the new tooth, the calcification of 

 p. m. ' is just Ix^ginning. i. I is developing, and can be seen in specimen 

 No. 38' far back in the alveolar cavit}' under the root of d. i. i, but is not 

 visible in the figure. 



In figuie 38r, a colt of two years, calcification has begun in all the 

 ]XMnian(4it teeth except /. ^. The crowns of the deciduous molars are 

 nearl\' worn away, while the roots are being absorl^ed by the growth of 

 the ])r(4n()lars which have now attained a considerable size. m. -, the 

 first j)erman(Mit tooth to erupt, has been in wearing about aj'earandis 

 just beginning to develop roots, m. - has cut through the gum and is 

 very slightly worn. The alveolar cavity below^ the eye, is now lodging its 

 last young tc^iant, m. '-, which by the time it is full grown will have 

 m()V(Ml nearly two inchc^s anterior to its present position. 



SHEDDING THE^TEETH 



Bl^FOUE the deciduous molars are shed the crowns are almost en- 

 tirely woin away on the one side, while the roots are absorbed by 

 the new teeth on the other, so that there is only a small fragment 

 of tooth really lost. The time of shedding ma}' vary a number of months : 

 At three years approximately, d. m. I and •! are shed, exposing the grind- 



'On exhibition in wall case. 



