642 CHIROPTERA 
account of the number of their upper incisors, supposed to be 
always four, the thoracic position of the mamme, 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 mammze 
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, 
while 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, we 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, we may accept the view of Professor Huxley that they 
should merely be regarded as exceedingly modified Insectivora. 
So thoroughly, however, has this adaptation for flight been 
carried out that of all animals the Bats are the least terrestrial, not 
one of them being equally well 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 follows 
from this arrangement that when a Bat is on the ground it rests on 
all fours, having the knees directed upwards; while, 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 where it 
can hitch itself up by the claws of the hind legs in its usual position 
when 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 vertebra differ 
very slightly in number and form throughout the species. The 
general number of the dorso-lumbar vertebre is 17, of which 12 
are dorsal; the cervicals are very broad, but short from before 
backwards, their breadth being due to the great transverse 
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 
