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 p6s- 
terior surface or dorsum (pl. 122, fig. 10) is convex, and divided into two 
unequal parts by a ridge or spine (jig. 10”). This spine, arising gradually 
from the margin of the scapula, increases in height as it proceeds forward, 
and becoming flattened above and below. It terminates in an eminence 
named the acromion process (jig. 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 swpra-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 (jigs. 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 (fig. 12") leads from the glenoid cavity, 
this being situated at the convergence of the two coste. The glenoid 
cavity (fig. 12”) is supported on a contracted neck; it consists of a shallow 
coneavity, in which plays 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 humerus or brachium (pl. 122, fig. 8 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 extremity 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 (jig. 3*) and the lesser (fig. 3°). Between 
these tubercles is the deep groove for the long tendon of the biceps muscle. 
The body 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 méernal condyle (fig. 3°), 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 depressions, 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. 
735 
