THE HUMERUS. 159 



fresh state it is converted into a foramen or closed canal by tendons which are inserted 

 upon these parts. Through it plays the tendon of the M. biceps, the one which represents 

 the " long" or " glenoid " head of the muscle in man. By Straus-Durckheim (A. I, 512), 

 the canal is called " coulisse bicipitale." 



410. Capitellum (humeri) The radial head, external or outer condyle (Fig. 80, 46, 6). 

 The distal end of the bone presents a smooth saddle-shaped surface, the caudal border 

 of which is raised, and the cephalic border rounded. As seen from the ventral aspect, this 

 arthral surface is nearly equally divided by a slight ridge, and the convex caudal portion 

 is the capitellum. This surface narrows as it is continued over the distal end of the bone, 

 so that its shape, if extended in a plane, would be approximately lanceolate or pear-shaped, 

 with a distinct emargination at the cephalic side of the base. 



With the capitellum articulates the fossa at the proximal end of the radius ; this end, 

 unfortunately, being likewise named capitettum. It would be well if anatomists could 

 agree to call one of these parts capitellum and the other capitulum. 



411. Caput (humeri) Articulare The arthral or anatomical head of the humerus. 

 The smooth convex arthral surface of this part hardly appears in this view of the bone, 

 but is shown in Fig. 71. In man it is distinguished from the non-arthral surface of the 

 rest of the Ext. proximatis by a furrow or constriction, the anatomical neck. In the cat, 

 this neck is not clearly denned. 



412. Crista Deltoidea The deltoid ridge " Crete deltoi'clienne externe," Straus- 

 Durckheim (A, I, 513) (Fig. 46, 68, 69). This is a narrow, nearly straight, and in well 

 marked adult humeri sharply defined raised line extending from the tubercle for the 

 insertion of the M. micostalis (Fig. 69) at the base of the trochiter on the cephalic aspect 

 of the proximal extremity distad and ventrad, to lose itself on the third fourth of the ven- 

 tral border. The sharpness which characterizes its proximal portion disappears at about 

 the middle of the bone. 



413. Crista Pectoralis The pectoral ridge " Crete deltoi'dienne anterieure," Straus- 

 Durckheim (Fig. 46, 69). This name is applied by us to the ill defined rough line upon 

 the proximal two thirds of the ventral aspect of the humerus. 



This and the Crs. deltoidea converge distad, but cease to be distinct before meeting. 

 The long triangular interval between them is called by Straus-Durckheim (A, I., 513), 

 " empriente deltoi'dienne." Mivart applies (B, 92, Fig. 53), the name deltoid ridge to what 

 seems to correspond to this interval, and inaccurately states that the two parts of the 

 M. deltoideus above mentioned are inserted upon it. 



414. DiaphysisThe shaft (Fig. 46, 30, 68-71). Although the shaft of the humerus 

 may be generally described as approximately cylindrical, it is slightly compressed, so that 

 at any point its cephalo-caudal diameter is less than its dor so -ventral. It is slightly 

 curved so as to present a ventral convexity. 



For convenience of description, the entire bone may be said to consist of a subcylindrical 

 shaft and enlarged extremities. Strictly speaking, however, the diaphysis includes all 

 but the proximal and distal epiphyses, and these are less extensive than the regions desig- 

 nated as extremitates. In a young animal the proximal epiphysis separates along an 

 undulating line passing distad of the caput articulare and the tubercle for the insertion of 

 the M. micostalis. The greatest length of the epiphysis equals only about one eighth of 

 the length of the entire humerus, whereas the Ext.proximalis includes about one fifth. The 

 distal epiphysis also includes merely so much as bears the arthral surfaces with the epi- 

 trochlea and epicondylus, whereas the proximal limit of the Ext. distalis embraces also the 

 Fm. epitrochlcare. 



Upon the caudal aspect of the diaphysis, near the junction of the first and second 

 fourths, and nearer the ventral than the dorsal border, is to be seen, with adult humeri, a 



