Anatomy of the Alligator, 28^ 



29. Pronator quadratus*. 0"43 oz. 



30. Supinator radii longus*. 0'42 oz. 



31. Extensor carpi radialis longior. 0*17 oz. 



32. Extensor carpi radialis brevior. 0"16 oz. 



33. Supinator radii brevis*. None. 



34. Extensor digitorum longus {qu. 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 jaAv. 

 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 lower jaw rests upon the mud of 

 the bank on which it lies. 



A. Aristotelis apertor oris. 1"34 oz. O. from the up^er 

 surface of the posterior process of the angle of the lower jaw. 

 I. into the outer fourth of the occipital ridge. 



B. Pterygoideus (clausor oris). 17*90 oz. O. from the 

 under surface of the posterior process of the angle of the lower 

 jaw. I. into the back 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 (a). 3"30 oz. 0. from the tips 

 of the spinous processes of all the cervical vertebrge. I. into 

 and below the occipital ridge. 



E. Cervico-spinal occipital (/3). 2'32 oz. O. from the sides 

 of the spinous processes of all the cervical vertebrae. 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 : — 



0. The origin of the muscle. 



1. 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 joining (C) the centre of the joint with the points (0) 



* See note §, antea. 



