MAMMALS. 387 



complete zygomatic arch, while as generally there are no frontal- 

 postorbital processes. The clavicle is present, and the ulna is 

 rudimentary. The brain is small and smooth. The sense of 

 touch is highly developed, the wings being important in this 

 respect, while in many species a peculiar dermal sensory appa- 

 ratus, the ' nose-leaf,' is developed upon the snout. The shape 

 of this, as well as that of the ears, is very variable, and is util- 

 ized in classification. The teeth are closely similar to those of 

 the insectivores ; the milk dentition is poorly developed, and 

 in some instances is lost before birth. The intestine is short 

 shortest in the insectivorous species ; a caecum rarely occurs. 

 The left lateral lobe of the liver is very large, and a gall bladder 

 is present. 



About four hundred species of bats are known, all nocturnal, 

 and usually gregarious in their habits. Frequently the colonies 

 are found to be composed of individuals of one sex, the sexes 

 only coming together at the breeding-season. There is some 

 evidence to .show that the males, at least in certain species, take 

 part in nursing the young. Fossils are rare ; they first appear 

 in the eocene. No fossil frugivora are known. 



SUB-ORDER i. ANIMALIVORA (MICROCHIROPTERA). 



Small bats with acutely cuspidate molars, index finger reduced, usually 

 with a single phalanx, no claw ; stomach simple, intestine short ; outer and 

 inner edges of ear not meeting below ; tail, when present, connected with 

 the interfemoral membrane. 



The old-world RHINOLOPHID.E, with a nose-leaf, i \, p f or f , and a 

 long tail, includes about fifty species. Rhinolophus occurs in Europe, 

 Asia, and Africa ; Hipposiderus, Asiatic. Rhinolophus occurs in the 

 eocene of France. Closely allied are Nycteris and Megadenna of Asia, in 

 which a tragus is developed in the ear. The VESPERTILIONID.E have a 

 long tail, lack the nose-leaf, and have a tragus to the ear and a variable 

 number of teeth. Plecotus, with an American representative, has i f, c |, 

 p, | m f ; Antrozous, from California, i \, c \, p \, m f. Vesperugo, the 

 largest genus of bats, is cosmopolitan, one species ( V. serotinns} inhabiting 

 both continents. The teeth are / f or i, c \, p f to i, ;// f . Atalapha (i |, 

 c 1' P I or \-> m f)' exclusively American. Vespertilio (i f , c -J-, p -|, m f), 

 cosmopolitan. Vesperugo, eocene, Wyoming. Thyroptera, Brazil. KM- 

 BALLONURID^:, tropical or subtropical, the middle upper incisors large and 

 close together, no nose-leaf; a distinct tragus, and obliquely truncate muz- 



