FREE APPENDAGES — MAMMALS 



291 



Amphibian limb now faces the rear, the hinge being transverse to 

 the axis of the body. To bring the digits of the manus so that they 

 point forwards, the fore arm has a twist 

 in the opposite direction, the radius cross- 

 ing the ulna so that digit i is on the medial 

 side of the appendage (fig. 301). Some 

 (e.g. Ungulates) move the hmb like a 

 pendulum in a single plane; in others (the 

 extreme occurring in man) it maybe swung 

 in almost every plane, this freedom of 

 motion at the shoulder being correlated 

 with greater capacity of rotation of ulna 

 around the radius, so that in man the hand 

 can be turned through 180°, either palmar 

 or dorsal side being downwards. There is .:, t^. , . 



'^ , _ I-IG. 315. — Diagram of torsion 



less torsion of the hind hmb, but, on the of fore-arm bones (Butschli, 



,111,1 • j-r i- 'lo). A is the primitive con- 



Other hand, there is more modification, dition with the elbow pointing 



chiefly by fusion, here. outwards; B with the elbow 



, directed backwards as in Mam- 



The humerus, short in Ungulates, mais, the limb parallel with the 



boscidia and swimming mammals, is ^^^e of the body. 



usually as long as the fore arm, rather slender and sHghtly curved. 



The head is somewhat roller-like in the primitive orders, and the limb 

 moves in a plane parallel with the axis of the body; else- 

 where it is hemispherical, giving the Hmb greater 

 freedom of motion. Both tuberosities are well devel- 

 *oped, especially in digging genera (moles, anteaters, etc.), 

 accompanied by a shortening of the whole Hmb. The 

 tuberosities are long crests in some Primates and bats. 

 The distal end of the humerus has one or two rollers for 

 the ulna (when two, separated by a groove), and a hemis- 

 pherical capitular head for the head of the radius. The 

 epicondyles are connected with inner and outer articular 

 'Surfaces, and on the posterior side is a pit or groove 

 (often perforate) between the condyles, to receive 

 the olecranon. An entepicondylar foramen is com- 

 mon (fig. 316) though lacking in Cetacea, recent 



Ungulates, most rodents and bats, and some other forms including 



man. 



Fig. 316. — 

 Humerus of 

 Dasypus; the 

 arrow passes 

 through the 

 e n t e picondy- 

 lar foramen. 



