45 
Pectoralis (Figure 8, p.) . This was probably the most powerful muscle 
of the brachium. It originated from the coracoid, sternum, and perhaps 
the ventral portions of the anterior ribs, and converged to the radial tuber- 
osity of the humerus. The strong development of radial crest and tuber- 
osity indicates good mechanical advantage for this muscle. It served, as 
it were, to pull down the distal end of the humerus, thus actually elevating 
the trunk. 
Dorsalis scapulas (presumably equivalent to the scapular portion of 
the deltoid) (Figure 8, d. s.). This is believed to have originated from the 
external surface of the scapula dorsal to a low, oblique ridge, which runs 
from the posterodorsal to the anteroventral angle of the bone. The inser- 
tion apparently was on the dorsal (extensor) side of the humerus, near the 
base of the radial tuberosity. Probably not a very powerful muscle, it 
served to flex the shoulder joint and rotate the humerus. 
Scapulo-huvieralis posterior (teres major). It appears that this muscle 
originated from the external surface of the scapula ventral to the ridge 
described under dorsalis scapulae, and was inserted in the ulnar tuberosity 
of the humerus. It served to adduct the humerus, and, with the dorsalis 
scapulae, to flex the shoulder joint without rotation. 
Brachialis anticus (humero-antibrachialis) (Figure 8, 6.a.). There are 
two divisions of this muscle in Sphenodon, and probably there were two in 
the ceratopsians. The origin of one branch may be located in the depres- 
sion on the flexor side of the humerus, at the base of the radial tuberosity. 
The other division probably originated from the ridge-like margin of the 
humerus distal to the radial tuberosity. The insertion would be on the 
preaxial side of the radius and ulna, near their proximal extremities. The 
function was essentially the same as that of the biceps. 
Biceps brachii (coraco-antibrachialis) (Figure 8, 6.6.). This muscle 
ran along the flexor side of the humerus from coracoid to proximal ends of 
radius and ulna. It is difficult to estimate the probable size, but as it was 
the main flexor of the limb, it must have been large. 
