50 OSTEOLOGY OF THE HORSE 



Division. — Into a body and two extremities. 



Body.— Angular, with expanded flattened sides, superiorly ; 

 contracted and rounded, inferiorly. From its upper, fore, and 

 outer part, projects the tuberosity; whose point is roughened by 

 the insertion of the levator humeri. The outer side of the body is 

 excavated and smooth ; it is occupied by the humeralis externus : 

 the inner side is rather prominent and roughened, and exhibits a 

 small scabrous eminence, which receives the tendons of the latis- 

 simus dorsi and teres major ; also, lower down, we find the 

 medullary foramen, pointing downwards. 



Superior extremity — Larger than the inferior, presents 

 for consideration a head and four tubercles. — The head is the 

 hemispherical smooth part projecting posteriorly ; it is designed 

 for articulation with the glenoid cavity of the scapula, which it 

 much exceeds in extent of superficies, and thereby obtains more 

 freedom and variety of motion. Into the irregular and indented 

 groove by which the head is surrounded, is fixed the capsular 

 ligament. Anteriorly, the head is surmounted by the tubercles : 

 the three directly in front are anti-articular, and have between 

 them two smooth grooves, which, as well as themselves, are 

 covered by cartilage, and altogether serve as a pulley for the ten- 

 don of the flexor brachii to play over. The outer articular 

 tubercle is joined by a protuberant ridge with the tuberosity. 

 The fourth, or outer tubercle, serves to guard against dislocation. 



Inferior extremity — Displays a specimen of the diar- 

 throdial or pulley-like articulation. It consists of two condyles, 

 distinct from each other posteriorly, being there separated by a 

 deep ovoid fossa, into which is received the olecranon of the 

 ulna ; but united, inferiorly and anteriorly, into a broad semi- 

 cylindrical articular surface, divided by a prominence encircling 

 its middle into two depressed compartments, of which the inner 

 has twice the breadth of the outer, and bounded by two lateral 

 prominent edges : furthermore, the condyles, of which the inner 

 is larger and more projecting behind as well as before, meet at 

 an angle above the fossa, and there run into union with the 

 body. There are also two scabrous pits above the articular sur- 

 faces in front, which, like the cavity behind, occasionally receive 

 processes of the bone below. 



Connexion. — The head of the humerus is adapted to the glenoid 

 cavity of the scapula ; the condyles are fitted into concavities upon 

 the upper extremity of the radius. 



Development. — In the young bone, the head, condyles, and 

 tubercles are epiphyses. 



