THE FASCIAE AND MUSCLES OF THE OEBIT. 



453 



Nerve-Supply. The muscle is supplied by the superior division of the oculo-motor nerve. 

 Actions. It elevates the upper eyelid and antagonises the action of the orbicularis oculi 

 muscle. 



ORBICULARIS OCULI 



\ 



RECTUS 

 SUPERIOR 



LEVATOR PALPEBR.E 

 SUPERIORIS 



Mm. Recti. The recti muscles are four in number superior, inferior, medial, 



and lateral. They all arise from a 



membranous ring surrounding the 



optic foramen, which is separable into 



two parts a superior common tendon, 



giving origin to the superior and 



medial recti and the superior head of 



the lateral rectus ; and an inferior 



common tendon, giving origin to the OBLIQUUS 



medial and inferior recti and the in- SUPERIOR 



ferior head of the lateral rectus. The 



two origins of the lateral rectus muscle 



are separated by the passage into the 



orbit of the oculo-motor, naso-ciliary, 



and abducent nerves. Forming flat- 

 tened bands which lie in the fat of the 



orbit around the optic nerve and eye- 

 ball, the four muscles end in tendons 



which pierce the fascia bulbi, and are 



inserted into the sclera about eight 



millimetres (three to four lines) behind 



the margin of the cornea. 



The superior and inferior recti are 



inserted in the vertical plane slightly 



medial to the axis of the eyeball ; the 



lateral and medial recti in the trans- 

 verse plane of the eyeball ; and all are attached in front of the equator of the 



eyeball. 



M. Obliquus Superior. The obliquus superior arises from the margin of the 



optic foramen between the rectus superior and rectus medialis. It passes forwards, 



as a narrow muscular band, medial to the rectus superior, and at the anterior 



margin of the orbit 

 forms a narrow ten- 

 don which passes 

 through a special 

 fibrous , pulley 

 (trochlea) attached 

 to the roof of the 

 orbit. 



Its olirection is 

 then altered, and 

 passing laterally, 

 between the tendon 

 of the superior 

 rectus and the eye- 

 ball, it is inserted 

 into the sclera be- 

 tween the superior 

 and lateral recti, 

 midway between 



FIG. 400. MUSCLES OF THE EIGHT ORBIT (from above). 



OBLIQUUS SUPERIOR 



LEVATOR PALPEBR.E SUPERIORIS (cut) 

 V RECTUS SUPERIOR 



RECTUS LATERALIS 



Oculo-motor 

 nerve 



Naso-ciliary 

 nerve 

 Abducent nerve 



OBLIQUUS INFERIOR 



RECTUS INFERIOR 



the 



FIG. 401. MUSCLES OF THE LEFT ORBIT (from lateral aspect). 



margin of the cornea and the entrance of the optic nerve. 



Obliquus Inferior. The obliquus inferior arises from the medial side of 

 ' of the orbit just behind its anterior margin, and lateral to the naso- 

 lacrimal groove. 



t forms a slender rounded slip, which curls round the inferior rectus tendon. 



30 & 



