OSTEOLOGY AND SYNDESMOLOGY. 29 



culi of the subscapular muscle. Above and below these is a smooth flat 

 surface for the attachment of the serratus magnus. The external or pos- 

 terior surface or dorsum {pi. 122, fig. 10) is convex, and divided into two 

 unequal parts by a ridge or spine {fig. 10*). This spine, arising gradually 

 from the margin of the scapula, increases in height as it proceeds lorward, 

 and becoming flattened above and below. It terminates in an eminence 

 named the acromion process {fig. 10^). The external surface of this process 

 is roughened, while near the apex is seen the articulation with the clavicle. 

 Above the spine is the supra-spinatus fossa, filled by the supra-spinous 

 muscle. The infra-spinatus fossa, below the spine, is larger. In the supe- 

 rior border or costa of the scapula is seen a notch, the supra-scapular 

 {fig. 10*), converted into a foramen by ligaments; through this passes the 

 supra-scapular nerve. From the anterior part of this border, in front of the 

 notch, there arises the coracoid process {figs. 10^, 11^); this overhangs 

 the upper and inner part of the glenoid cavity. The base of the scapula, 

 or the posterior border, is the longest margin of the bone. The anterior, 

 inferior, external, or axillary costa {fiig. 12 ') leads from the glenoid cavity, 

 this being situated at the convergence of the two costrc. The glenoid 

 cavity {fig. 12°) is supported on a contracted neck ; it consists of a shallow 

 concavity, in which plaj^s the head of the humerus. In life or the fresh 

 subject, this cavity is deepened by the fibrous glenoid ligament. 



The arm is composed solely of the hmnerus or h-achium {pi. 122, fig. 3 c). 

 It is the longest and largest bone in the upper extremity, and presents a 

 body or shaft, with two extremities. The upper or scapular extremit}^ is 

 the larger, and consists of the head, neck, and two tubercles. The head 

 {fig. 18) is hemispherical, inclined upwards, inwards, and backwards ; it is 

 smooth, and covered with cartilage for articulating with the glenoid cavity 

 of the scapula. The neck is the slightly contracted line or furrow round 

 the head ; it is roughened for the attachment of the capsular ligament. The 

 tuberosities are two, the greater {fig. 3') and the lesser {fig. 3"). Between 

 these tubercles is the deep groove for the long tendon of the biceps muscle. 

 The hodij or shaft of the humerus is thick and round above, twisted in the 

 middle, expanded and somewhat triangular below. The lower extremity 

 of the humerus {fig. 14) is flattened, elongated transversely, and twisted a 

 little forwards. It presents internally the internal condyle {fig. S"), which 

 is very prominent; externally is the external condyle {fig. 3 '), not so promi- 

 nent as the internal, and situated lower down. Between and below these 

 condyles is a series of articulating eminences and depi-essions, partly turned 

 forwards : they consist externally of a small round head of the radius, 

 internal to which is a slight depression, corresponding to the margin of the 

 radius. Internal to this is a sharp semicircular ridge, extending round the 

 lower end of the bone, separating the radius and ulna. Next comes the 

 trochlea^ for articulation with the ulna. At the anterior extremity of this 

 trochlea is a depression for the reception of the coronoid process, and at the 

 posterior is another, for receiving the olecranon process of the ulna. The 

 bone between these two depressions is thin and transparent, and sometimes 

 deficient by absorption. 



73Ö 



