28o ZOOTOMY. 



fore-arm is, like that of the humerus, external, the same 

 border comes to be internal in the distal end of the fore-arm 

 and in the manus, the dorsal surfaces of which look, on the 

 whole, forwards. 



84. The humerus, a long bone consisting of a shaft 

 and of two prominent extremities, and having its long 

 axis directed from the glenoid cavity downwards and back- 

 wards, so that its originally dorsal surface looks upwards and 

 backwards, its ventral surface downwards and forwards, its 

 pre-axial border outwards, and its post-axial border inwards. 

 The proximal extremity presents, dorsally, a rounded head 

 for articulation with the glenoid cavity ; pre-axially, a large 

 projection, the greater tuberosity ; post-axially, a smaller 

 projection, the lesser tuberosity; and between the 

 tuberosities a depression, the bicipital groove. On the 

 anterior (ventral) surface of the proximal end of the shaft is 

 the deltoid ridge. The distal extremity presents a large 

 puUey-Hke surface, or trochlea, for the articulation of the 

 ulna and radius, and a smaller pre-axial surface, or capi- 

 tellum, for the radius only (see §§ 85 and 86) ; a deep 

 olecranon fossa on the posterior (dorsal) side, for the 

 reception of the olecranon process of the ulna, perforated 

 by a small supra-trochlear foramen ; a small pre-axial 

 external condyle just outside the capitellum; and a 

 larger post-axial internal condyle, similarly situated with 

 regard to the trochlea. In the young rabbit the extremities 

 of the humerus consist of separate bones, or epiphyses. 



85. The radius, or shorter bone of the fore-arm, slightly 

 curved forwards, and so situated that its true dorsal surface 

 looks forwards and slightly upwards, and its pre-axial 

 border inwards. Its proximal extremity or head presents 

 a double articular surface for the pulleys of the humerus : 

 its distal extremity, a pair of slight concavities for the 



