314 ANATOMY OF VEKTEBRATES. 



lodged in the socket, which extends backward beyond the last 

 molar tooth to the base of the coronoid process. The most im- 

 portant character by which the incisors of this anomalous Lemur 

 differ from those of the Rodentia is the entire investment of ena- 

 mel, which is, however, thicker upon the front than upon the back 

 part of the tooth. The molar teeth are four on each side of the 

 upper jaw, and three on each side of the lower jaw, implanted 

 vertically and in parallel lines. The molars are of simple struc- 

 ture, with a continuous outer coat of enamel, and a flat subelliptic 

 grinding surface. The upper ones are of unequal size, the first 

 being the smallest, and the second the largest. In the lower jaw 

 the inequality is less, and the last molar is the least. The first and 

 last molars above have but one root ; the second and third have 

 each three roots. The first lower molar has two roots ; the second 

 and third have each a single root. The adult dental formula is — 



.1.1 o 1.1 8.3 



l Li ;C 0^0.0 ;Wt 3.3 = 18 - 



The deciduous dentition is — 



.2.2 1.1 . 1.1 



l U ;c o7o' dm p= 12 ' 

 The second upper incisor and canine, and the lower milk-molar, all 

 which are very minute, are not replaced ; the first true or perma- 

 nent molar follows so speedily the deciduous one that, being ' in 

 place ' therewith, it has been reckoned with the milk-dentition. 1 

 The lower jaw is modified to give strength to the muscles 



wielding the enormous and 

 powerful incisors by the low 

 position of the condyle, analo- 

 gous to that in Plagiaulax and 

 other carnivorous Mammals, 

 contrasting with its high posi- 

 tion in true Rodents and Kan- 

 garoos. 



The Avahi, or woolley Le- 

 mur (Lichanotus laniger, fig. 

 250), has the incisors of the 

 lower jaw large and limited to a 

 single pair, but far from show- 

 ing the proportions of those in Chiromys : the upper incisors are 

 in two pairs, as in the milk-dentition in Chiromys, and are small. 

 The dental formula in the Slow Lemurs ( Stenojis, Tarsius) is — 



.2.2 1.1 3.3 3.3 

 i 2.2' C T.T ; ^3T3 ;m 3:3 =:36 - 



The first upper incisor is larger than the second. 



Dentition of Woolley Lemur. 



