TEE ANTEBIOB LIMBS. 



ulna. In the petitadactylous animals, a3 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 vlna is in, 

 increased proportion as the animal exclusively employs its inferior 

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

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

 or at least 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 treea, 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 some 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-arni in 

 Buminants 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 radioulnar 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 invadiug that portion of the inter- 

 osseous ligament placed above the superior vascular arcade. 



In the Pig, 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 bones of the fore-arm are nearly equal in volume, 

 and are slightly crossed 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 touch by their extremities, and to this effect oflfer: 1, 

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

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

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



D Fore-foot, ob hand.— 1. Carpal 6o»es.— The carpus of the 

 Piq like that of Man, contains eight 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 ot the lower 

 row it is observed that the first corresponds with the twc external 

 metacarpals, the second with the great internal metacarpal, the third 

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

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

 relations with 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 me acar- 

 pals; 10, Principal metacarpals; 11, External digit; 12, Internal 

 diafit. 



87 



Fig, 52. 



-J 



FORE-AKM AND FOOT 

 OF THE OX ; FBOMT 

 VIEW. 



