THE ANTERIOR LIMBS. 



87 



ulna. In the pentadactylous animals, as Man, the Cat, etc., on 



the contrary, this is a veritable long bone which equals, or even 



exceeds, the radius in volume. 



2. The closeness of union between the radius and ulna is in 



increased proportion as the animal exclusively employs its interior 



extremity for standing or walking. Thus, in Solipeds and Rumi- 

 nants, and Pachyderms in general, the two bones are consolidated, 



or at li ast united, by an interosseous ligament, and in so firm a 



manner that they can only execute very obscure movements on 



each other. The anterior limb of these animals is indeed only 



used to support the body on the ground. In those, on the con- 

 trary, which may employ it to dig up the soil, climb on trees, etc., 



or as an organ of prehension, the radius and ulna are merely 



joined at their extremities by an articulation, which permits them 



to move upon one another with the greatest facility. Rodents, the 



majority of the Carnivora, and the quadrumana, are so provided ; 



but it is in Man that the relative independence of the two bones is 



carried to the highest degree. No animal can so easily execute 



the movements of pronation and supination of the hand, which 



are determined by the play of the two bones of the fore-arm on 



each other. 



To the indication of these fundamental characters may be 

 added s"ine details on a few particular and important points. 



In all the domesticated animals other than Solipeds, the ulna 

 is developed from three ossifying centres, extends the whole length 

 of the radius, and concurs to form the articular surface correspond- 

 ing to the carpal bones. It is an elongated bone in Ruminants, 

 and a long bone, hollowed by a medullary canal, in the Pig and 

 Carnivora. 



The inferior articular surface of the bone of the fore-arm in 

 Ruminants is cut obliquely from above to below, and from with- 

 out to within. In 'these animals we find the radius very flat from 

 before to behind, the bicipital tuberosity scarcely noticeable, and 

 two radio ulnar arcades united externally by a deep fissure. The 

 union of the two bones is more intimate than in the Horse, for the 

 ossification always finishes by invading that portion of the inter- 

 osseous ligament placed above the superior vascular arcade. 



In the P*gr, the ulna is flattened from before to behind, and 

 spread out on the posterior face of the radius, which it almost 

 completely covers. Its olecranon is very prominent. In the Dog 

 and Cat, the two Ixmes of the fore-arm are nearly equal in volume, 

 and are slightly cro sed in an X fashion. The superior extremity 

 of the ulna is thicker than its lower extremity ; it is nearly the 

 opposite of this in the radius. Movable on one another, these 

 bones only touc-h by their extremities, and to this effect offer : 1, 

 Above, on the ulna, a concave articular surface, the small sig- 

 moid cavity, and on the radius a rounded hinge-like facet; 2, 

 Below, on the radius, a concave surface, and on the ulna a convex 

 one. 



D. FORE-FOOT, OR HAND.!. Carpal bones. The carpus of the 

 Pig, like that of Man, contains eij^ht bones four in each of the 

 rows. The second bone of the upper row corresponds with the ulna, 

 and to a small extent with the radius. In the bones of the lower 

 row, it is observed that the first corresponds with the two external 

 met:u arpals, the second with ihe great internal metacarpal, the third 

 with the preceding and the small internal metacarpal. The fourth, 

 or trapezium, terminates inferiorly by a blunt point, and has no 

 re'atious w.th the metacarpal bones, because the thumb is entirely 

 undeveloped in this animal. 



1, Olecranon ; 2, Body of the ulna ; 3, Body of the radius ; 4, 5, 6, 

 First, second, and third bones of the upper row of the carpus ; 7, 8, 

 First and second bones of the lower row ; 9, Rudimentary metacar- FORE-ARM AND FOOT 

 pals; 10 X Principal metacarpals ; 11, External digit; 12, Internal OF THE ox; FRONT 

 digit. VIEW. 



