OSSEOUS SYSTEM OF MAMMALIA. 81 



The ulna, and the radius, in the fore-arm of the Simise, resemble those 

 of Man ; excepting that the radius is the stoutest of the two : the humerus 

 is long and slender ; and the clavicle has a less decided flexure than 

 in the human subject. 



The hands, then, of the Simiae are rude imitations of those of Man, 

 organized as instruments of climbing. In the Cheiroptera, or Bats, a wing- 

 handed race, which emulate ihe bird in traversing the regions of the air, the 

 modification of the hand is such as to fit it for an organ of flight : the 

 carpus is reduced to a comparatively small space, and consists of two 

 bones in the first row, and four in the second. Of the first row the 

 internal bone is by far the largest, and supports the first metacarpal 

 bone ; the bones of the second row are compressed laterally, and, with 

 the exception of the second, are elongated ; each supports a metacarpal 

 bone. The metacarpal bones, setting aside that of the thumb, are of 

 singular length and slenderness ; as are, also, the phalanges of the 

 fingers, which taper gradually to a point, like the extremity of a fishing- 

 rod, and having their joints so constructed as to fold laterally. The 

 thumb, on the contrary, is short, and comparatively stout ; consisting of 

 a metacarpal bone, based upon the large bone of the carpus, and two 

 phalanges, the last of which is terminated by a strong hooked claw. The 

 fore-arm is remarkable for its great length, and consists essentially of the 

 radius only ; for the ulna is reduced to a mere stylet, situated behind the 

 radius at its commencement, and there entering into the elbow-joint: free 

 at this part, it often merges, at its apical portion, into the radius ; its 

 degree of development, however, varies in different species ; and in some, 

 as the common Bat, it can scarcely be said to exist. In the Flying Lemur, 

 or Colugo (Galeopithecus), a similar modification of the ulna is found. In 

 this animal, the ulna, though more developed than in the Bats, is still rudi- 

 mentary : it is separated superiorly from the radius, for about a third of 

 its length, whence it insensibly blends with the radius, and terminates 

 before reaching its extremity. The humerus in the Bats is long, with a 

 round voluminous head ; the clavicles are large, as are also the scapulae, 

 the acromion processes of which are long, and directed forward. Over 

 the anterior extremities of the Bat, thus modified (fig. 81), is stretched a 

 semi-transparent membrane, which encloses the fingers, leaving the thumb 

 almost free : it embraces the whole of the arm, and thence extends to 

 the hinder limbs, and often between the latter, so as to include the tail. 

 This membranous wing, to which the bones act as stretchers, is capable of 

 being folded up while the animal is at rest ; on the ground the Bat shuffles 

 itself along awkwardly, buf can climb about the rugged bark of a tree, or 

 the wires of a cage, with considerable facility, using the strong claw of its 

 thumb, and its hinder feet (the toes of which are also furnished with 

 hooked claws), in its progressive motions. The use of the wings, or of 



VOL. I. M 



