644 CHIROPTERA 



species the ribs are much flattened, and in some they are partially 

 ankylosed by their contiguous margins. 



The skull is subject to considerable structural variations, 

 even within the limits of a single family. Postorbital processes 

 to the frontals are found only in the Pteropodidce and some 

 Nycteridce and Emballonuridce. Pteropus leucopterus and Pteralopex 

 are peculiar in having the orbit completely surrounded by 

 bone. A slender zygomatic arch is present, except in some of the 

 Phyllostomatidce. 



The milk-teeth are peculiar in that they are utterly unlike those 

 of the permanent series. They are slender, with sharp recurved 

 cusps ; and as a rule are shed at an early period (in the Rhino- 

 lophidce before birth), but may coexist with some of the fully 

 developed permanent teeth. The permanent teeth are subject to 

 great variation of form, although they always have distinct roots. 

 In the Insectivorous types they are acutely cusped, the cusps in 

 those of the upper jaw being arranged in a more or less distinct W ; 

 but in the frugivorous forms, like the Pteropodidce and some of the 

 Phyllostomatidce, the molars are longitudinally grooved or hollowed 

 out. 



The pectoral girdle maintains a very constant type. Thus the 

 clavicle is very long, strong, and curved ; and the scapula large, 

 oval, triangular, with a long curved coracoid process. The humerus, 

 though long, is scarcely two-thirds the length of the radius. The 

 ulna is rudimentary, its proximal extremity, which articulates with 

 but a small part of the humerus, being ankylosed to the radius ; 

 and immediately beyond the joint it is reduced to a slender splint- 

 like bone, extending about as far as the middle of the radius. In 

 all species a detached sesamoid bone exists in the tendon of the 

 triceps muscle. The radius is very long, in some species actually 

 equal to the length of the head and body. The proximal row of 

 the carpus consists of a single bone formed by the united scaphoid, 

 lunar, and cuneiform ; which, with the extremity of the radius, 

 forms the radio-carpal joint. In the distal row the trapezium, 

 trapezoid, and magnum vary in size in the different families, the 

 unciform appearing to be the most constant, and the pisiform being 

 generally very small. 



The manus is always furnished with five digits. The first, 

 fourth, and fifth digits consist of a metacarpal and two phalanges ; 

 but in the second and third digits the number of phalanges is 

 different in certain families. The pollex always terminates in a 

 claw, which like the proximal phalanx is best developed in the 

 frugivorous species. In most of the frugivorous Pteropodidce the 

 second digit is provided with a claw; but in all other Bats this and 

 the remaining digits are unarmed. In the genus Tricenops alone a 

 very peculiar short bony process projects from the outer side of 



