Mammalia: Classification 739 



Order 6: CHIROPTERA. Flying mammals. The wing (Fig. 547) 

 is a web of skin supported largely by the forelimb, extending back 

 along the side of the body to the hindlimb, and continued behind the 

 hindlimbs as the interfemoral membrane, which may or may not 

 include the tail. All parts of the skeleton of the forelimb are much 

 elongated except the hallux, which is not involved in the wing. The 

 four digits posterior to the hallux support a large area of the wing. The 

 hallux always bears a sharp claw. The pes projects freely beyond the 

 edge of the wing and each of its five digits bears a sharp claw. Tail 

 may be long, short, or lacking. Low keel on sternum (see p. 518). 

 Dentition complete and not highly specialized. Cerebral cortex not 

 convoluted. 



Two Suborders are recognized : 



Suborder MEGACHIROPTERA. Large frugivorous bats. Claw 

 on second digit of manus, as well as on the hallux; tail, if present, not 

 enclosed in interfemoral membrane. 



These are the "fruit bats" or "flying foxes" (Pteropus) of the 

 warmer parts of the Eastern Hemisphere. 



Suborder MICROCHIROPTERA. Small bats, chiefly insectivo- 

 rous, but the South American vampire bites mammals and sucks their 

 blood. No claw on second digit of manus. Tail, if present, enclosed in 

 interfemoral membrane. 



Numerous species of bats. Distribution world-wide. 



Order 7: RODENTIA. Mostly small, chiefly herbivorous. Teeth 

 specialized for gnawing hard substances: incisors, one pair in upper jaw, 

 one pair in lower, long and chisel-like, their enamel usually thick only 

 on the front surface of the crown, thin or lacking elsewhere, thus en- 

 suring maintenance of a sharp cutting edge; no canines; wide gap 

 (diastema) between incisors and cheek-teeth, the latter being flat- 

 topped and adapted for crushing and grinding. 



The articulating surface (glenoid) on which the lower jaw r works 

 is usually elongated anteroposteriorly, allowing the lower jaw to be 

 moved backward and forward. When in its posterior position, the 

 upper and lower cheek-teeth meet, but the incisors do not, the lower 

 passing up behind the upper (Fig. 548). When the incisors are to be 

 used for gnawing, the lower jaw must be moved forward so that the 

 edges of upper and lower incisors meet exactly — meanwhile upper and 

 lower cheek-teeth do not meet. The animal cannot gnaw r and chew at 

 the same time. There is more or less transverse motion of the lower 

 jaw when the cheek-teeth are being used for grinding. 



Locomotion is usually plantigrade. In the manus the pollex may be 

 reduced or absent, and in the pes there may be even more reduction in 



