310 



ANATOMY OF VERTEBRATES. 



forming the fangs. The dentinal compartments (vol. i. fig. 237) 

 are rarely well defined ; in the large canines of the Centetes they 

 are subhexagonal. 



o 



The deciduous teeth of the Moles and Shrews are uterine, i.e., 

 are developed and disappear before birth. They are extremely 

 small, and are all of the most simple form. In the fetal Sorex 

 araneus calcification of the papillary exposed pulps of the teeth, 

 which are succeeded by the first and second premolars, proceeds 

 to a very slight extent, and these microscopic rudiments appear 

 to be absorbed rather than shed. The deciduous incisors arc 

 further advanced before their displacement, and present the form 

 of equal-sized dentinal spicula, tipped with enamel, attached by 

 the opposite end to the gum, and not exceeding -j-Jth of an inch 

 in length ; the number of the uterine series of teeth is 4:4. 



o o o 



Iii the volant Insectivora, or Bats, the canines are always 

 present in both jaws, of the normal form, and with slightly 

 variable proportions. The molar series never exceeds -|:f , and is 

 divisible into premolars and true molars ; the latter are bristled 

 with sharp points in the great bulk of the Cheiroptera. The inci- 

 sors are the most variable teeth ; they may be entirely wanting, or 



be present in the numbers of '.' l w ~'^ ; they are always very small, 



and, in the upper jaw, commonly unequal, and separated by a 

 wide median vacancy. In the genus Chilonycteris, the mid- 

 incisors above and the outer ones below have the crown notched ; 

 the mid-incisors below have two notches, producing three lobes 

 on the cutting border. Taking the common simple-nosed Bat 



( Vespertilio murinus) as a 

 type of this Insectivorous 

 group, we find its dental 

 formula to be 



245 



.2.2 



1.1 



3.3 



3.3 



-= 38. 



In the leaf-nosed Bats 

 (Phyllostoma, fig. 245) the 

 incisors are f:|, the mid 

 pair above being large and 

 laniariform ; the canines 

 are well-developed in both 

 jaws. The second premo- 

 lar above has a large, tried ral, pointed crown. The first and second 

 molars have two large external, and three small internal cusps. 

 The dentition of the blood-suckino; Bats deviates, as might be 



t_? y ^^ 



Dentition of leaf-nosed Bat (riujllostoma). 



