THE MUSCLES 51 



N. ophthalmicus profundus (Vj) although an important cutaneous 

 branch of this nerve crosses its dorsal side (see p. 139). 



Innervation: By N. trochlearis (fourth cranial nerve). 



Function : See below. 



M. obliquus inferior (m.o.i.). 



Like its superior counterpart this muscle arises from about the 

 middle of the cart, antorbitalis. It passes in a postero-ventral direc- 

 tion and is inserted on the ventral side of the eyeball. It has rather 

 a long insertion on a line approximately at right angles to the optical 

 axis, so that the lateral fibres are much shorter than the mesial ones. 



Innervation : From the R. inferior N. oculomotorius. 



Function: The oblique muscles serve to rotate the eyeball about 

 the optical axis. Both are, however, very weak. 

 M. retractor bulbi {or ocult) (m.rt.b.). 



This is by far the most powerful of all the eye-muscles. It takes 

 its origin in part from the lateral process of the parasphenoid that 

 lies under the otic capsule, and in part from the orbito-sphenoid at 

 the inner ventral angle of the orbit. Its fibres spread out to form a 

 cone around the optic peduncle and are inserted on the mesial surface 

 of the bulbus oculi within the ring formed by the rectus muscles. The 

 cone is, however, not complete, since the edges of the muscle are not 

 quite in contact mesially in the region of the anterior rectus muscle. 



Attached to the M. retractor bulbi is a strong tendon connecting 

 it with the eyelids. This tendon forms a broad sheet posteriorly 

 but bifurcates anteriorly to allow for the passage of the anterior 

 rectus muscle. When this tendon is pulled the edges of the eyelids 

 are brought together and the eye closed, and although there appear 

 to be smooth muscle elements in the upper lid rendering it capable 

 of independent movement, nevertheless the M. retractor bulbi and 

 the tendon must be regarded as the chief agents effecting the closing 

 of the eye, which is thus made to occur simultaneously with the 

 retraction of the bulbus oculi. 



Innervation : From the N. abducens (sixth cranial nerve). 



Function: To retract the bulbus and to close the eyelids as de- 

 scribed above. 



3. Muscles of the Fifth Nerve. 



M. levator mandibulae as a whole. 



Elevateurs de la machoire inferieure . . . Meckel (18 18). 



Temporalis .... Cuvier (1835); Owen (1866). 



Adductor mandibulae ..... . Driiner (1901). 



Masseter Wilder (189 1). 



