454 



THE MUSCULAR SYSTEM. 



and passes between ' the lateral rectus and the eyeball, to be inserted into the 

 sclera between the superior and lateral recti, and farther back than the superior 

 oblique muscle. 



M. Orbitalis (O.T. Miiller's muscle) is a rudimentary bundle of non-striated muscular fibres 

 bridging across the inferior orbital fissure and infra-orbital groove. It is supplied by fibres from 

 the sympathetic, and may have a slight influence in the protrusion of the eyeball. 



Lacrimal gland 



Frontal nerve 



Supra-orbital nerve 



Lacrimal nerve 



Nerves to rectus superior and 



leva tor palpebrae superioris, 



from oeulo-motor nerve 



Trochlear ner 



RECTUS LATERALI 



Abducent nerv 



Oculo-motor nerve (inferior 

 division) 



Ciliary ganglion 



Nerve to rectus inferior, from 



oculo-motor nerve 



Nerve to obliquus inferior, 



from oculo-motor nerve 



Supra-trochlear nerve 



LEVATOR PALPEBR.E 

 SUPERIORIS 

 RECTUS SUPERIOR 



OBLIQUUS SUPERIOR 



Anterior ethmoidal branch 

 of naso-ciliary nerve 

 Infra-trochlear branch 



RECTUS MEDIALIS 



Nerve to rectus medialis, from 



oculo-motor 



.Ophthalmic artery 



Optic nerve 



Long ciliary nerves 



RECTUS INFERIOR 



OBLIQUUS INFERIOR 



FIG. 402. SCHEMATIC REPRESENTATION OF THE NERVES WHICH TRAVERSE THE CAVITY OF THE RIGHT ORBIT. 



Nerve-Supply. The muscles of the eyeball are supplied by the third, fourth, and sixth 

 cerebral nerves. The trochlear (fourth nerve) supplies the obliquus superior; the abducent 

 (sixth) supplies the rectus lateralis ; the oculo-motor (third nerve) supplies the others recti, 

 superior, inferior, and medialis, and obliquus inferior. 



Actions. The six muscles inserted into the eyeball serve to move the longitudinal axis .J 

 of the eyeball upwards, downwards, medially, and laterally, besides causing a rotation of the 

 eyeball on its own axis. The following table expresses the action of individual muscles. It must 

 be remembered that, while similar movements occur simultaneously in the two eyeballs, the ,j 

 horizontal movements may, by adduction of the muscles of both sides, cause convergence of the 

 axes of the two eyeballs for the purposes of near vision. 



Muscles of Mastication. 



The muscles of mastication comprise the masseter, temporal, external an( 

 internal pterygoids, and buccinator (described above). 



M. Masseter. The masseter is the most superficial. Covered by the paroti- 

 gland on the side of the face, it has an origin which is partly tendinous an' 

 partly fleshy. It arises in two parts : (1) superficially from the inferior border c 

 the zygomatic arch in its anterior two-thirds, and (2) more deeply from the dee 

 surface of the zygomatic arch in its whole length. The superficial fibres ai 



