46 
Triceps (anconaeus) (Figure 8, tr.). This probably had four origins, 
one from the anterodorsal margin of the scapula, one from the postglenoid 
margin of the coracoid, and one from each side of the humerus. These all 
converged on the olecranon process of the ulna, forming a powerful ex- 
tensor of the antibrachium. 
All recent students of the Ceratopsia are agreed that the humerus was 
normally borne in a more or less horizontal position. In conjunction with 
this interpretation the radius and ulna are usually placed nearly vertical, 
maxing an angle of 90 degrees or less with the humerus. This, however, 
is the position of extreme flexion ; that the limb was capable of marked ex- 
tension is shown by the strong olecranon process of the ulna and the large 
olecranon fossa of the humerus. Probably the greatest flexion occurred as 
the limb reached the forward position. Then the thrust to the body would 
be given by rotation and adduction of the humerus, with extension of the 
elbow joint. In the forward stroke the limb would be lifted clear by flexion 
of the shoulder joint and extension of the limb. 
HIND LIMB 
The pelvic musculature in the ornithischian dinosaurs has been re- 
constructed by Romer (/), w 7 ith special reference to the ornithopod Thes- 
celosaurus This form is very generalized compared with the ceratopsians, 
and the different structure of the pelvis no doubt was accompanied by 
differences in musculature. 
Figuie 9 . Cliasmosaurus belli (Lambe), restoration of the musculature, left lateral view: b ., 
Hiccinator; o.a., brachialis anticus; b.b., biceps brachii; cdc., capiti-dorsi-clavieularis; 
cn., cleiaonumeralis; d.s., dorsalis scapulae; e.c.r.b., extensor carpi radialis brevis; e.d.c.b., 
extensor digitorum communis brevis; f.c.r., flexor carpi radialis; f.c.u flexor carpi 
ulnaris; /.d.c.p.. flexor digitorum communis profundus; flexor tibialis; g, gastrocne- 
mms; 17. llio-ftbuJams; it., ilio-tibialis; l.d., latissimus dorsi; Ig. d., longissimus dorsi; 
l.s., levator scapulae; m., massetericus; o.e., obliquus externus; p., pectoralis; per., 
peroneus; pl.tn., platysma myoides; pm., parieto-mandibularis; r., rectus; sc. , supracora- 
coideus; ss„ serratus superficialis; supinator; t.a., tibialis anticus; im., temporalis; 
xr ., triceps; X 
. pi-o -tibialis (rectus femoris of mammals) (Figure 9, it.) . The probable 
origin of this muscle was from the dorsolateral margin of the ilium, from 
the anterior end to the so-called anti-trochanter. The muscle would tra- 
verse the knee joint and be inserted in the head of the tibia. This was the 
