88 INTRODUCTION. 



the phalanges of the three fingers ; and two rudimentary lateral bones, 

 of which the outermost is extremely small. The fingers consist of the 

 ordinary number of phalanges, f: of these the first row is short, and 

 consolidated with the metacarpal bones ; the second phalangal row is 



elongated, as are also the ungueal 

 phalanges : these latter are greatly 

 compressed and curved ; and the 

 pulley-like articulation, formed be- 

 tween each and the preceding pha- 

 langal bone, is very deep and narrow, 

 so as to produce the utmost firmness. 

 Nature has aimed at rigid, unyield- 

 ing strength, and has obtained the 



Arm and Hand of the Sloth. o.humerus; 6, radius; c, ulna; TCSult sllC Wished. The long 



d. carpus; e, metacarpus ;/, phalanges. 01 i i i r i i 



of the Sloth being thus furnished 



with hooks, it can reach to a distant branch, and there fix itself with 

 facility ; or, while clinging to one branch, can draw towards itself another, 

 loaded with buds, fruits, or leaves, which offer a grateful repast. 



Turning to the Rodentia, with a view to the general structure of the 

 hand and arm, the osseous framework of these parts is more perfect, as 

 might be expected, than in most of the lower Mammalia. The Squirrel, 

 and the Beaver, and others of this order, use the arm with great facility, 

 and are able to hold their food between their paws while they nibble it 

 with their teeth : they have no opposable thumb, but the fingers are usually 

 free ; and the hand of many of them, especially of such as climb, bears 

 a great similarity to that of the Marmozet Monkeys of America.* The 

 fore-arm is endowed with the liberty of pronation and supination (though 

 in some, as the Porcupine and Agouti, for instance, this power is limited) ; 

 and the majority of this species, as far as the author has had an opportunity 

 of examining, have a tolerably perfect clavicle. In the Cavies and the 

 Porcupines it is most rudimentary ; the first row of carpal bones usually 

 consisting of three ; in the Hares of four : the second, or anterior row, 

 usually of five, sometimes of four. The metacarpus generally consists of 

 an inner small bone, supporting the phalanges of a minute thumb ; and 

 of four long bones, of which the two middle extend beyond the rest. 

 As habits and modes of life differ so greatly among the Rodentia, the 

 development and form of the phalanges are accordingly modified. 



Passing from the Rodentia to the truly carnivorous races of which 

 the feline group may be regarded as the type it may be stated, that, 

 with a corresponding restriction in the movement of the shoulder and 



* A Squirrel sitting up, engaged in devouring a nut, its favourite food, holds the fruit between the 

 rudimentary thumbs of the paws brought together, and not between the fingers, as might be 

 supposed. 



