724 MAMMALIA. 



before backwards, and furnished with many cusps. The lower are 

 pectinated, the flattened crowns being penetrated by numerous vertical 

 slits, and the outer of the two upper pairs have double roots. Two 

 species of this genus live in the forests of the Malayan region. They 

 are nocturnal, and feed on leaves and fruit. The dentition is —— . 

 There are numerous skeletal peculiarities. 



{ 



Order Chiroptera. Bats. 



Bats are specialised Mammals related to Insectivores. 

 They have the power of flight, the fore-limbs being modified 

 as wings. The wing is formed by a fold of skin which 

 usually begins from the shoulder, extends along the upper 

 margin of the arm to the base of the thumb, thence between 

 the long fingers, and along the sides of the body to the hind- 

 legs or even to the tail. Contrasted with the wing of a 

 bird, that of a bat has a rudimentary ulna beside a long 

 curved radius, a wrist with six bones, five free digits, four 

 of which have very long metacarpals, while the thumb is 

 short. The phalanges are usually reduced to two. The 

 pectoral girdle is strong ; there is a long curved clavicle, a 

 large triangular scapula, a long coracoid process ; the pre- 

 sternum bears a slight keel on which are inserted some of 

 the muscles used in flight. The thumb is always clawed ; 

 the other digits are unclawed, except in most frugivorous 

 bats, where the second digit bears a claw. 



The hind-limb is relatively short and weak, the pelvic 

 girdle is also weak, and in most cases the pubic symphysis 

 is loose in the males, unformed in the females. The knee is 

 turned backwards like the elbow; the ankle has a cartil- 

 aginous prolongation or calcar, which supports the fold of 

 skin between limb and tail ; the five toes are clawed. 



The vertebral column is short; there is little mobility 

 between the vertebrae ; neural spines are absent behind the 

 third cervical, except in Pteropids ; the caudal vertebras are 

 very simple. The ribs are usually flat. The maximum 

 dentition is ||^| ; the milk-teeth are very different from the 

 permanent set. All the bones are slender, and the long 

 bones have relatively large medullary canals. 



The cerebral hemispheres are smooth, and leave the cere- 

 bellum uncovered. The spinal cord is at first very broad, 



