100 INTRODUCTION TO CLASSIFICATION. 



series of the teeth is uneven and interrupted. The hallux 

 is large, while the second digit is always peculiarly modi- 

 fied, and sometimes rudimentary. 



In this sub-order alone are the further characters found, 

 that the lachrymal foramen is situated on the face; the 

 orbit and temporal fossa communicate freely, as in the 

 three succeeding orders; the clitoris of the female is 

 perforated by the urethra ; and more than one pair of teats 

 may be present. 



2. The INSECTIVOBA. The dentition varies. Usually, there 

 are more than four incisors in each jaw, and the molars have 

 sharp and pointed cusps. 



The hallux possesses a claw, and has no marked freedom of 

 adduction and abduction. 



In all genera but one there are well-developed clavicles. 



The so-called Flying Lemurs (Galeopithecus), the Hedgehogs, 

 the Shrews, and the Moles belong to this order. 



3. The CHEIROPTERA. The dentition varies, but well- 

 developed canines are always present. 



The clavicles are strong and long. The fore-limbs are much 

 longer than the hind limbs, and have the four ulnar digits pro- 

 longed. At least three of these are nailless. A prolongation 

 of the integument, or " patagium," unites the prolonged digits 

 together, and the arm with the body. 



The hallux resembles the other digits. There are one or 

 two pair of pectoral teats. The penis is pendent, and the 

 testes remain in the abdomen. 



To this order the Bats belong. 



4. The RODENTIA . There are never more than two incisors 

 in the lower jaw, and usually only two, but sometimes four, 

 in the upper. These incisors have persistent pulps, and con- 

 tinue to grow in adult life. 



There are no canines. The molars vary in number from 

 2.2 6.6 

 2.2 1 ' KB' 



The hallux, when present, resembles the other digits, and 

 the number of teats varies. 



The Eats, Hares, Squirrels, &c., constitute this order. 



