638 



GHOEDATA. 



tail, inchules the lower extremities to the foot, and extends thence 

 to the fingers, leaving the thumb free. Fingers 2-5 are enormously 

 elongated and support the membrane. Since flight requires 

 strong muscles, the sternum develops a small keel, recalling that 

 of birds, for the attachment of the large jiectoral muscle. In con- 

 nexion with the flying powers the clavicle is stroTig. The patagiuni 

 is the seat of a very acute tactile sense, by means of which blinded 

 bats can flj^ among all kinds of obstacles without disturbing them. 

 The enormous ear conchs and a noticeable nose leaf, widely dis- 

 trilnited through the group, also have marked tactile powers. In 

 the pectoral position of the mammary glands and in the discoidal 

 placenta these animals resemble the primates. In temperate 

 regions bats hibernate during the winter. Tlie dentition is vari- 

 able, often fyff. Fossils occur in the eocene. 



Sub Order I. MICROOHIROPTERA, with insectivorous dentition, 

 only the thumb of the fore limbs clawed. VESPERXiLlONlDiE, tail long, no 

 nose leaf : Vesj)€rugo* Atalapha* Phyllostomid^, with nose leaf, trop- 

 ical America ; Desmodtis, the blood-sucking or vampyre bat. 



Sub Order II. MACHPvOCHIROPTERA (Frugivora), with smooth- 

 crowned molars, claws on thumb and first two fingers. Includes the flying 

 foxes, Pteropus, of the East Indies. 



Order IV. Rodentia. 



The rodents unite great similarity in appearance with a char- 

 acteristic dentition. The canines are absent, and the molars are 

 separated by a large gap (diastema) from the incisors (fig. 6G3). 



The latter are strong, chisel-like, 

 have jjersistent jjulps and grow at 

 the lower end as they are worn 

 away at the cutting edge. Since 

 only the front surface has enamel, 

 wear keeps them constantly sharp. 

 Usually there is but a single in- 

 cisor, and only in the Duplici- 

 dcntata is a second present in the 

 upiicr jaw. The molars are cus- 



pidate or have enamel folds and 

 frequently continue to grow 

 throughout life. T heir number is 

 frequently reduced, the -formulas 

 Many species have an inflected 

 angle of the jaw like that of nuirsnpials. The infraorbital canal 

 is a striking feature in Muridte and llystricid;\? (fig. 6G3, o), a 



Fk;. 1(03. — tSkuII of porcupine. (From 

 Schuiarda.) /, frontal: im^ proniaxil- 

 lary; h, temporal fossa continuous in 

 front with orbit; o, infraorhital fora- 

 men, enormous on account of the por- 

 tion of the massetep muscle which 

 liasses through it. 



varying between j-{[:!|] and }"'y^ 



