MUSCLES OF THE EYEBALL. 71 



iv. The rectus inferior is inserted into the under surface 

 of the eyeball : it is seen best from below. 



b. The obliqui muscles are a group of two small muscles 



which arise close together from the palatine bone at the 

 anterior end of the orbit, and run backwards to be 

 inserted into the eyeball. 



i. The obliquus superior is inserted into the dorsal 

 surface of the eyeball just in front of the rectus 

 superior : it is seen best from above. 



ii. The ohliquus inferior passes backwards beneath 

 the rectus internus, and is inserted into the eye- 

 ball between it and the rectus inferior : it is seen 

 best from below. 



c. The retractor bulbi, or choanoid muscle, is a funnel- 



shaped muscle which lies within the four recti and 

 embraces the optic nerve : it arises from the para- 

 sphenoid, and is inserted into the eyeball. It is best 

 exposed from below by carefully removing the recti 

 muscles. 



C. Muscles of the Hind-limb. 



If the frog's leg be stretched back parallel to the longitudinal 

 axis of the body, as in the act of swimming, we distinguish in 

 it ventral and dorsal surfaces, an outer border in which is the 

 projection of the knee, and an inner border along which is the 

 bend of the knee. The outer border, which corresponds to the 

 front of the leg in man, is called the extensor surface, inas- 

 much as the muscles which extend or straighten the leg lie 

 along this edge : the inner border is the flexor surface. The 

 "ventral "and "dorsal" surfaces only appear to be such in 

 consequence of the extreme obliquity of the pelvic girdle : they 

 are really anterior and posterior, and are better called preaxial 

 and postaxial : they correspond respectively to the inner and 

 outer surfaces of the human leg. If the foot be examined care- 

 fully, it will be seen that the first digit or " big toe " is on the 

 preaxial side, and hence may be called the preaxial digit: 

 while the fifth or " little toe " is on the postaxial side, and is 

 therefore the postaxial digit. 



