66 THE MUSCULAR SYSTEM OF THE FROG. 
iv. The rectus inferior: inserted into the under 
surface of the eyeball: seen best from below. 
b. The obliqui muscles: 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: inserted into the dorsal | 
surface of the eyeball just in front of the rectus 
superior: seen best from above. | 
“ii, The obliquus inferior: passes backwards beneath 
the rectus internus, and is inserted into the 
eyeball between it and the rectus inferior: 
seen best from below. 
$3 
c. The retractor bulbi, or choanoid muscle: 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 
seen from below by carefully removing the recti 
muscles, 
C. The 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. 
