sensory adaptations of bats. 137 



Morphological Peculiarities axd Relationships. 



Bats, constituting the order Chiroptera, are more sharply 

 marked off from their nearest relatives than any other group of 

 mammals. Their closest affinities are with the order insectivora 

 which includes such animals as the moles and shrews. However, 

 the separation is a wide one and no known fossils are in any way 

 intermediate between the two orders. 



The most important modification is the adaptation to flight. 

 The changes in structure correlated with the habit of aerial loco- 

 motion are the following : The fore limb and pectoral bones and 

 muscles are increased in size and the hind limb and pelvis are 

 reduced. The axis of the hind limb is rotated so that the knee 

 projects backward instead of forward. The digits of the fore 

 limb are lengthened to form a support for the wing membrane. 

 A thin, flexible membrane extends from the sides of the body to 

 the tips of the fingers and from in front of the fore arm to the 

 hind Hmbs and usually includes the space between the latter and 

 the tail. 



Other structural peculiarities are as follows : The carpus is 

 reduced or almost wanting. The first digit (thumb) of the manus 

 is short, nearly free from the wing membrane, opposable, and 

 terminated by a curved claw. The other digits of the manus are 

 long, slender, included in the wing membrane and not terminated 

 by nail or claw. The pes has five short, subequal digits, each 

 with a curved claw. The mammae are pectoral and there is usu- 

 ally but one pair, although a few species have two pairs. The 

 cerebral lobes are without convolutions, and the cerebellum is 

 relatively large. The ear conch has a slender internal lobule 

 called the tragus in most species, and in several families there 

 are foliaceous appendages of skin about the nostrils. 



These structural modifications are worthy of note because they 

 are correlated with the characteristic habits of the animals. 

 Walking or running, after the manner of most animals, is seri- 

 ously impeded by the lengthening of the fingers, the presence 

 of a membrane joining the limbs, and by the reversal of the di- 

 rection of the knee flexure. Locomotion on solid surfaces is 

 therefore the rare exception and flight is the common method of 

 progression. 



