10 HANDBOOK OF ANATOMY 



The bicipital groove passes down its anterior surface, directed 

 slightly to the inner side, and gradually fades away. About 

 the middle of the inner and outer surfaces are rough surfaces 

 for the insertions of the coraco-brachialis and deltoid respectively. 

 On the posterior surface a shallow groove the musculo-spiral 

 groove winds from within outwards, separating the origins of 

 two heads of the triceps. The lower end of the shaft is flattened 

 and expanded into two condyles, of which the inner is larger 

 than the outer. From each of these condyles a ridge runs up 

 for about one-third of the shaft. Between the two condyles are 

 the trochlear and capitellar surfaces for the articulation of the 

 ulna and radius respectively. The trochlea is a grooved surface, 

 which winds spirally round the inferior end of the bone and 

 shows on the posterior surface. The capitellum is on the outer 

 side of the trochlea, a small, rounded surface which shows only 

 on the anterior surface. Above the trochlea, both anteriorly 

 and posteriorly, are small, round fossse, the coronoid and ole- 

 cranon respectively, for articulation with the processes of the 

 ulna in extreme flexion and extension. 



The humerus articulates, by means of its rounded head, with 

 the glenoid cavity of the scapula, and at its inferior end with 

 the ulna and radius. 



Ossification. The primary centre for the shaft appears before 

 birth. Secondary centres for the two tuberosities and the head 

 appear during the first few years of life, and these three first 

 unite, forming an epiphysis, which unites with the shaft as a 

 whole in adult life. A similar arrangement is observed with 

 the condyles and articular surfaces of the lower end, which 

 also form a separate epiphysis. 



The Ulna, the inner bone of the forearm, is a long bone 

 with a shaft and two extremities. The head is formed of two 

 processes, the olecranon posteriorly and the coronoid anteriorly. 

 The olecranon process forms a continuation of the shaft, and is 

 hollowed out anteriorly for articulation with the trochlear sur- 

 face of the humerus. Tne coronoid process juts out from the 

 anterior surface of the shaft, and its upper surface is in con- 

 tinuation with the anterior surface of the olecranon process, the 

 two between them forming the semilunar notch or sigmoid fossa.. 



