502 



HUMAN ANATOMY. 



THE METAMERIC MUSCLES. 



A. THE AXIAL MUSCLES. 



As has been pointed out, the history of the anterior two groups of myotomes, 

 suppUed by cranial nerves, differs somewhat from that of the remaining ones, and 

 it is convenient, therefore, to consider the muscles derived from these myotomes 

 separately from the rest. 



I. THE ORBITAL MUSCLES. 



1. Levator palpebrae superioris. 



2. Rectus superior. 



3- 



Rectus internus. 



7. Obliquus inferior. 



4. Rectus inferior. 



5. Rectus externus. 



6. Obliquus superior. 



The most anterior of the persistent myotomes are three in number, supplied by 

 the oculo-motor, trochlear, and abducent nerves. They give rise to the muscles 

 situated in the orbit. 



I. Levator Palpebr^ Superioris (Fig. 516). 



Attachments. — The levator palpebrae superioris is a rather slender muscle 

 which lies in the greater portion of its course immediately beneath the periosteal 



It arises at the back of the orbit, a short distance 



above the upper margin of 



lining of the roof of the orbit. 



Fig. 514. 



Tendinous loop 

 for sup. oblique 



Superior oblique, 

 distal part 



Internal rectus, 



Superior oblique,, 

 proximal part 



Optic nerve. 



ator palpebrae sup. 

 Upper tarsal plate 

 Palpebral fissure 



perior rectus 



Inferior oblique 



External rectus 



palpebrae superioris 



Ocular muscles seen from above after removal of roof of orbit ; elevator of 

 uppf-r eyelid has been cut and reflected forward. 



the optic foramen, and is 

 directed forward, broad- 

 ening as it goes, to be in- 

 serted by a broad aponeu- 

 rosis principally into the 

 upper border of the tarsal 

 plate of the upper eye- 

 lid, the uppermost fibres 

 mingling somewhat with 

 those of the palpebral 

 portion of the orbicularis 

 oculi. 



The aponeurosis by 

 which the levator inserts 

 into the tarsal plate is 

 largely composed of non- 

 striated muscular fibres, 

 which constitute what has 

 been termed the orbito- 

 palpebral muscle. This 

 is triangular in shape, 

 with the truncated apex 

 united to the levator and 

 with the base attached 



to the external palpebral 

 raphe, the tarsal plate of the upper eyelid, and the internal palpebral ligament. 



Nerve-Supply. — From the oculo-motor nerve. 



Action.— To draw the upper eyelid upward and backward. 



Relations. — Immediately above the levator palpebrae superioris, between it and 

 the periosteum of the roof of the orbit, are the trochlear and frontal nerves and the 

 supra-orbital vessels. Below it rests upon the medial half of the rectus superior. 



