596 MAMMALS. 



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 with 

 long metacarpals on the four fingers. The shoulder-girdle 

 is very strong, there is a long curved clavicle, a large tri- 

 angular scapula, a long coracoid process ; the presternum 

 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 cartilaginous 

 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 Pteropidae, the caudal vertebrse are 

 very simple. The ribs are usually flat. The maximum 



dentition is 2^ ; the milk-teeth are very different from the 



3133 

 permanent set. All the bones are slender, and have large 



medullary canals. 



The cerebral hemispheres are smooth and leave the 

 cerebellum uncovered. The spinal cord is at first very 

 broad, but narrows rapidly behind the neck. The sense of 

 touch is remarkably developed in the hot skin of the wing, 

 the large mobile external ears, the whisker hairs of the 

 snout, afld in the strange plaited " nose-leaves " around the 

 nostrils. Even when deprived of sight, hearing, and smell, 

 bats will fly about in a room without striking numerous 

 wires stretched across it. 



The temperature of the body is high. The testes are 

 abdominal or inguinal ; the penis is pendent. The uterus 

 is simple, with cornua generally short. There is usually but 

 one offspring at a time. The mammae are thoracic, gener- 

 ally post-axillary. As in Insectivora, the yolk-sac forms a 

 provisional yolk-sac placenta, and. the allantoic placenta is 

 discoidal and deciduate. 



Fossil Chiroptera occur in Upper Eocene strata, but are 

 quite like the modern forms. 



