642 CHIROPTERA 



account of the number of their upper incisors, supposed to be 

 always four, the thoracic position of the mamma 3 , and the pendent 

 condition of the penis. Many other zoologists, taking into con- 

 sideration the placental characters and the form of the uterus, have 

 followed him ; but it is evident that the situation of the mammae 

 is related to the necessarily central position of the young during 

 flight, the shortness of the uterine cornua, observable in so many 

 species, to the generally uniparous gestation requiring less room, 

 Avhile the discoidal deciduate placenta is equally present in and 

 characteristic of the Insectivora, many species of which also have 

 the penis pendent. Thus, the reasons for maintaining the Bats in 

 this high position being disposed of, Ave find in the low organisation 

 of their brain a proof of their inferior status ; while furthermore, 

 although they differ widely from all other mammals in external 

 form, it is evident that this is only the result of special adaptation 

 to aerial locomotion ; and, taking into account their whole bodily 

 structure, Ave may accept the vieAV of Professor Huxley that they 

 should merely be regarded as exceedingly modified Insectivora. 



So thoroughly, hoAvever, has this adaptation for flight been 

 carried out that of all animals the Bats are the least terrestrial, not 

 one of them being equally Avell fitted for progression on the earth. 

 This is due to the hind as well as the fore limbs being pressed into 

 the service of aerial locomotion. Thus the hind limb is so rotated 

 outwards by the wing-membrane that, contrary to what obtains in all 

 other vertebrates, the knee is directed backwards, and corresponds 

 in position to its serial homologue the elbow. It necessarily f oIIoavs 

 from this arrangement that when a Bat is on the ground it rests on 

 all fours, having the knees directed upwards ; Avhile, in order to 

 bring it into a position for forward progression, the foot rotates 

 forwards and inwards on the ankle. Walking under these circum- 

 stances is at best only a kind of shuffle, and that this is fully 

 recognised by the animal is evidenced by its great anxiety to take 

 wing, or, if this be impracticable, to ascend to some point Avhere it 

 can hitch itself up by the claws of the hind legs in its usual position 

 Avhen at rest. 



The bones of the skeleton are characterised by their slender- 

 ness and the great size of the medullary canals in those of the 

 extremities. The vertebral column is short, and the A^ertebra? differ 

 very slightly in number and form throughout the species. The 

 general number of the dorso-lumbar vertebra? is 17, of which 12 

 are dorsal ; the cervicals are very broad, but short from before 

 backAvards, their breadth being due to the great transA r erse 

 diameter of the spinal canal rendered necessary by the compara- 

 tively large size of the spinal cord, which, after giving off the nerves 

 to the fore limbs and thorax, rapidly diminishes in size, and in the 

 lumbo-sacral region is reduced to a fine thread. Except in the 



