Anatomy of the Alligator. 289 
29. Pronator quadratus*. 0°43 0z. | 
30. Supinator radii longus*. 0°42 oz. 
31. Extensor carpi radialis longior. 0°17 oz. 
- 32. Extensor carpi radialis brevior. 0°16 oz. 
_ 83. Supinator vail brevis*. None. 
34. Extensor digitorum longus (gu. ext. oss. metacarpi 
pollicis). 0°10 oz. 
35. Extensor carpi ulnaris. 0°24 oz. 
III. Muscles of the Jaws and Head. 
_ Herodotus and Aristotle state that the Crocodile, alone, 
moves the upper jaw, while other animals move the lower jaw. 
This statement is borne out by the muscular anatomy of the 
animal, which is capable of opening its mouth by lifting the 
upper jaw and head while its neat jaw rests upon the mud of 
the bank on which it lies. 
. A. Aristotelis apertor oris. 1°34 0z. O. from the upper 
surface of the posterior process of the angle of the lower jaw. 
I. into the outer fourth of the occipital gai 
B. Pterygoideus (clausor oris). 17°90 0z. O. from the 
under surface of the posterior process of the angle of the lower 
jaw. I. into the tack of the pterygoid plate and all round the 
floor of the orbit of the eye, forward. 
C. Masseter. 4°90 oz. 
D. Cervico-spinal occipital («). 3°30 0z. O. from the tips 
of the spinous processes of all the cervical vertebre. I. into 
and below the occipital ridge. 
E. Cervico-spinal occipital (8). 2°32 oz. O. from the sides 
of the spinous processes of all the cervical vertebra. I. into 
the occiput, below the insertion of the last (a). 
IV. Comparison of the. Pelvic. and Scapular Muscles. . 
The plane of motion in which any muscle moves a bone 
round the joint is defined by three points :— 
O. The origin of the muscle. 
I. The insertion of the muscle. 
_ C. The centre of motion of the joint. 
- The point I varies as the limb changes its position, while 
the points C and O remain absolutely fixed in the pelvis, and 
comparatively fixed in the shoulder or scapular joint. The 
lines joming (C) the centre of the joint with the points (O) 
* See note §, anted. 
