XU INTEODUCTIOK. 



radius, with which it coalesces about the middle. In all species a 

 detached sesamoid bone exists in the tendon of the triceps muscle, 

 and is generally found in skeletons. The radius forms, with the 

 humerus, almost the whole elbow- joint; it is very long, in some 

 species {Phyllorhina commersonii and Ph. tricuspidata, e. g.) as long 

 as the head and body. 



The proximal row of the carpus consists of a single bone (the 

 united scaphoid, lunar, and cuneiform bones), which, with the 

 extremity of the radius, forms the radiocarpal joint : in the distal 

 row the trapezium, trapezoid, and os magnum vary much in size in 

 the different families ; the unciform appears to be the most constant, 

 and the pisiform is generally very small. But the chief differences 

 in the bones of the carpus and their articulations are observable 

 between those of the Megachiroptera, in which the thumb and 

 second finger are so well developed, the latter generally with a 

 distinct claw, and the Microchiroptera, in which the same digits are 

 comparatively much smaller, and the second finger has a single 

 rudimentary phalanx only* unprovided with a claw. In the Mega- 

 chiroptera the trapezium is by far the largest bone in the distal row; 

 its inner surface is deeply grooved for articulation with the trochlear 

 extremity of the metacarpal bone of the thumb ; its distal extremity 

 fills up the space between the base of the metacarpal bones of the 

 thumb and first finger, with which it articidates, while its proximal 

 end forms a rounded head, which is received into a deep depression 

 between the united scaphoid and lunar bones. The trapezoid is very 

 small and quadrate above, articulating with the outer portion only 

 of the second metacarpal bone ; the os magnum is next in size to 

 the trapezoid, and the unciform is but slightly smaller than it ; the 

 pisiform is very small, with a circular upper extremity. In the 

 Microchiroptera, even in the frugivorous species of Phyllostomidce, 

 the trapezium is much smaller than either the os magnum or unci- 

 form, and does not much exceed the trapezoid in size, while its arti- 

 culation with the concave extremity of the metacarpal bone of the 

 thumb is very simple, and its proximal extremity is not received 

 into a deep concavity in the scapho-lunar bone ; the trapezoid has a 

 long wedge-shaped distal process, which, with the end of the trape- 

 zium, is received into the space between the extremities of the first 

 and second metacarpal bones, the latter almost wholly articulating 

 with it ; the unciform is as large as the os magnum, and the pisi- 



* With the single exception of Rhinoponui, in which the index finger has two 

 small phalanges {vide infra, p. xiii.). 



