THE BATS 79 



finger is joined at its tip to the third finger. In the insect- 

 eating bats it has never more than two joints, and sometimes 

 one, or none at all, and is pressed closer and closer to the strong 

 third finger until in some species its rudiment is hardly discernible 

 in the membrane. In the fruit-eating bats the hallux, or big toe, 

 is well developed and armed with a big claw ; so also is the fifth 

 toe. In one genus of bats the hallux is opposable to the other 

 toes, like the big toe in the hind feet in lemurs and monkeys. 

 The hind limbs are almost directed backwards at right angles 

 to the spine and pelvis in order to support the flying membrane. 

 In the fore arm the radius becomes a much-bowed and very 

 strong bone, while the ulna shrinks to a mere splinter. 



In the teeth there are these points to be noted : — The upper 

 incisors are never more than two in number on each side, while 

 the lower incisors may number three pairs. The earliest known 

 lemurs had three pairs of incisors in each jaw, but in all modern 

 lemurs, monkeys, and anthropoids the formula never exceeds two 

 pairs in each jaw. Some Insectivores possess the normal three 

 pairs in both jaws, but in that group there is a tendency towards 

 the loss and specialisation of the lower incisors. This is the 

 opposite to what prevails in the bats, in which, where a change 

 takes place, it is usually in the direction of diminishing the 

 number of upper incisors.^ 



The mammae are never more than two in number, and are 

 placed on the breast. In the external and internal organs of 

 generation the resemblance of the bats lies almost equally with 

 the Insectivora and the lower Primates. The brain is of low 

 development, and is that of an Insectivore. 



This order is divided into two clearly marked sub-orders, 

 the Megacheir opera (fruit-eating bats) and the Microcheiroptera 

 (usually insect-eating bats). The first of these sub-orders hardly 

 comes within the purview of this book, as no form of this group 

 has ever been known to exist in Britain or in any part of Europe. 



1 This tendency to increased degeneration in the lower incisors exists 

 to some extent in the fruit-eating bats, which also never possess more than 

 two pairs of incisors in either jaw. 



