Chap. VII] 



MUSCULAR TISSUE 



97 



Fig. 68. — Muscles of 

 Right Eyeball within 

 THE Orbit. Seen from 

 the front. 21, superior 

 rectus ; 22, inferior rectus ; 

 23, external rectus ; 24, 

 internal rectus ; 25, su- 

 perior oblique ; 26, inferior 

 oblique. 



ful ; by its contraction the eyebrows are elevated, the skin of the 



forehead thrown into transverse wrinkles, and the scalp drawn 



forward. The occipital acts in direct line 



with the frontal, and emphasizes its action. 

 Muscles of the face. — There are about 



thirty facial muscles ; they are chiefly 



small, and only a few are considered. We 



group them as : (1) Orbital muscles, (2) 



jNIuscles of mastication, and (3) Muscles 



of expression. 



Orbital muscles. — The orbit contains 



seven muscles; six of them are attached 



to the eyeball, and the seventh is attached 



to the upper lid. The six muscles attached 



to the eyeball are arranged in three oppos- 

 ing pairs. 



The superior and inferior recti. — These two muscles have their 



origin at the apex of the orbital cavity and pass straight forward 



to their insertion into the eyeball, the superior rectus in the 



middle line above, and the inferior rectus opposite it below. 

 Action. — Contraction of the superior rectus rolls the eye 



upward ; contraction of the inferior rolls the eye downward. 

 The internal and external recti. — These two muscles have their 



origin at the apex of the orbital cavity, and pass forward to their 



insertion into the eyeball, the 

 internal on the inner side, the 

 external on the outer side. 



Action. — Contraction of the 

 internal rectus draws the eye 

 inward toward the nose. Con- 

 traction of the external rectus 

 draws the eye outward. 



Superior oblique. — The su- 

 perior oblique muscle arises 

 from the apex of the orbit (the 

 same as the four recti), courses 

 forward to the upper and inner 



angle of the orbit, w^here it passes through a loop of cartilage. 



Then it bends at an acute angle, passes around the upper part 



Fig. 69. — Muscles of Eyeball. 

 Seen from side. 19, elevator muscle of 

 eyelid ; 22-26, same as in Fig. 68. 



