50 THE SALAMANDER 



Innervation: By the superior ramus of N. oculomotorius (third 

 cranial nerve). 



Function: See below. 



M. rectus posterior (m.r.p.). 



The abducent muscle arises as a fine tendon from the orbito- 

 sphenoid at about a third of its length from the posterior end, just 

 behind the M. rectus inferior. It passes obliquely postero-laterally, 

 ventral to the M. retractor bulbi, and is inserted in the postero- 

 lateral portion of the eyeball. Like all the rectus muscles it broadens 

 considerably towards its insertion. 



Innervation: From the abducent nerve (sixth cranial). 



Function: See below. 



M. rectus inferior (m.r.i.). 



The inferior rectus muscle also has a tendinous origin just anterior 

 to that of the posterior rectus and posterior to the anterior rectus. It 

 is considerably shorter than the muscle just described, and some- 

 what broader. It runs laterally, its fibres lying almost at right angles 

 to the axis of the skull. Its insertion occupies the ventral section of 

 the ambitus of the bulbus. 



Innervation: From the inferior ramus of the N. oculomotorius 

 (third cranial nerve). 



Function: See below. 



M. rectus anterior (m.r.a.). 



As mentioned above, the tendon of this muscle leaves the orbito- 

 sphenoid just anterior to that of the inferior rectus. Its fibres take 

 a direction practically at right angles to those of the former muscle 

 and lie close along the side of the skull. They are inserted on the 

 antero-mesial surface of the bulbus oculi. It is the largest and 

 strongest of the rectus muscles. 



Innervation: From R. inferior N. oculomotorius. 



Function : The function of all the rectus muscles is obviously to 

 rotate the eyeball in the horizontal and vertical planes at right angles 

 to its own optical axis. They are all relatively weak. 



M. obliquus superior (m.o.s.). 



Arises as a fine tendon from about the centre of the cartilago 

 antorbitalis of the nasal capsule. Its fibres run posteriorly and are 

 inclined slightly mesialwards. They are inserted on the antero- 

 dorsal portion of the eyeball just anterior to those of the M. rectus 

 superior. The muscle lies dorsal to the main portion of the 



