'////; MH TIL 



351 



at tho bottom of the infundilmlum. Nevertheless, the quantity accumulated 

 in this ,-nl-ilfviK- is imt always the same; we have seen it sometimes almost 

 null, mid on the other haiul wo possess incisors unworn, or nearly so, in 

 which the cavity is almost entirely obstructed by the crusta petrosa. We 

 are not aware that, up to the present time, any account has been taken of 

 differences when calculating the progress of wear; but it may be 

 imagined that they ought to influence in a sensible manner the period at 

 which effacement of the external dental cavity takes place. 



Fig. 159. 



INCISOR TEETH OF THE HORSE. DETAIUS Of ffTRCCTI ! 



1. A tooth in which is indicated the general shape of a permanent incisor, and tli. 

 |..irtii ular forms successively assumed by the dental tahl iu riisc<|ui-ii 

 frirtii.n. and the continued pushing outwards of these teeth; '_'. A virgin to.itli. 

 anterior and posterior beat; ; . LngitadiM] section of a virgin tooth, int. -u.l.- 1 

 to show the internal conformation and structun:. Nt t<> i-oinplicatc tin- li-uif. 

 the external cement, and that amassed in the infundihuliim, has not 

 exhibited. 4, Transverse section for the saint- pur]M.s>; .<. Ktn-irrling 

 '., (Vntr.il .'11.1111.1; .-, Dental star; </, Dentine; .', Deciduous tooth. 



All the characteristics just indicated Ix-li.n^ t-J tlio tleriduott* t /// 

 (Fig. 151), 5), except that th< y aiv smaller than the permanent; that tln-y 

 are of a shining milky-white colour, due to tho thinness or absence of the 

 a petrosa; that they show at tho point of union between the free 

 portion and tho root, a constriction named tho neck ; that their crown is tinely 

 striated, and not caimular, on tho anterior face : that the external cnl-1 



