BONES OF THE THORACIC LIMB 



147 



( 



times perforated. The proximal end unites with the shaft at three and a half 

 5'ears, the distal at one year. 



The radius is short and narrow, but thick. The shaft 

 increases in size from above downward. The greater part ^ 



of the posterior surface is in apposition with the ulna; this 

 part is marked by a vascular furrow w^hich runs downward 

 from the upper interosseous space, and has the nutrient 

 foramen at its proximal i.'W'X. The l)icipital tuberosity is 

 represented by a rough area. The distal end is relatively 

 large. Its carpal surface consists of concavo-convex facets 

 for the radial and intermediate carpal bones. There is a 

 wide shallow groove on the middle of the front. The 

 proximal end fuses with the shaft at one year, the distal 

 at three and a half years. 



The ulna is massive. It is much longer and con- 

 siderably heavier than the radius. The shaft is curved. 

 The anterior surface is convex and most of it is rough 

 and attached to the radius by the interosseous liga- 

 ment. There is a smooth area on the upper third, 

 which concurs with the radius in forming the upper 

 interosseous space, and is marked in its upper part 

 by the nutrient foramen. From this space a vascular 

 furrow passes downward to the lower part of the shaft, 

 where there is often a distal interosseous space for 

 the passage of vessels. The internal surface is exten- 

 sive, concave, and smooth. The external surface is 

 slightly convex, and its upper part is marked by an 

 oblique rough line or ridge. The proximal extremity is 

 large and is bent inward somewhat; its length is more 

 than one-third of that of the entire bone. The distal ex- 

 tremity is relatively small; it articulates with the ulnar 

 and accessory carpal bones, and is notched in front to 

 accommodate the ridge on the radius. The bone contains 

 a considerable medullary canal. The bone is consolidated 

 at three to three and a half years. 



The carpus comprises eight bones, four in each row\ 

 The bones of the proximal row resemble those of the ox, 

 with the exception of the accessory, which is more like 

 that of the horse, but has no external groove. The first 

 carpal is small, elongated from before backward, rounded, 

 and articulates in front with the second carpal. The latter 

 is high and narrow, and articulates with the second and 

 third metacarpal bones below. The third carpal articu- 

 lates with the radial and intermediate above, the third 

 metacarpal bone below. The fourth is the largest bone 

 of the row; it articulates with the intermediate and ulnar 

 above, the fourth and fifth metacarpals below, and bears 

 a tuberosity on its volar aspect. 



Four metacarpal bones are present. The first is 

 absent, the third and fourth are large and carry the chief 

 digits, while the second and fifth are much smaller and 

 bear the accessory digits. Their proximal ends articulate 

 Avith each other and with the carpus as indicated above, 

 solidated at about two years of age. 



i- » .'/ 



/ -^ 



'h- 



(^ 



Fig. 113. — Skeleton of 



FOEEARM AND MaNUS 



OF Pig, Antero-ex- 



TERNAL View. 



a, Radiu.s; h, ulna; c, 

 radial carpal; d, intermediate 

 carpal; e, ulnar carpal; /, ac- 

 cessory carpal; g, first carpal; 

 h, second carpal; i, third car- 

 pal; k, fourth carpal; l-o, 

 second to fifth metacarpal 

 bones; p-s, second to fifth dig- 

 its; 1, olecranon; 2, beak of 

 ulna (proc. anconeus); 3, semi- 

 lunar notch; 4, styloid process 

 of ulna; 5, styloid process of 

 radius; 6, distal epiphyseal 

 lines; 7, first phalan.x; 8, second 

 Ijhalanx; 9, third phalanx. 

 (Ellenberger-Baum, .\nat. d. 

 Haustiere.) 



The bones are con- 



