244 



MUSCLES AND FASCIAE. 



front of the optic foramen ; and is inserted, by a broad aponeurosis, into the upper 

 border of the superior tarsal cartilage. At its origin, it is narrow and tendinous; 

 but soon becomes broad and fleshy, and finally terminates in a broad aponeurosis. 

 Relations. By its upper surface, with the frontal nerve and artery, the peri- 

 osteum of the orbit ; and, in front, with the inner surface of the broad tarsal 

 ligament. By its under surface, with the Superior rectus ; and, in the lid, with 

 the conjunctiva. A small branch of the third nerve enters its under surface. 



Fig. 149. Muscles of the Right Orbit. 



The Rectus /Superior, the thinnest and narrowest of the four Kecti, arises from 

 the upper margin of the optic foramen, beneath the Levator palpebrae, and Supe- 

 rior oblique, and from the fibrous sheath of the optic nerve ; and is inserted, by a 

 tendinous expansion, into the sclerotic coat, about three or four lines from the 

 margin of the cornea. 



Relations. By its upper surface, with the Levator palpebrse. By its under 

 surface, with the optic nerve, the ophthalmic artery, and nasal nerve; and, in 

 front, with the tendon of the Superior oblique, and the globe of the eye. 



The Inferior and Internal Recti arise by a common tendon, the ligament of 

 Zinn, Avhich is attached round the circumference of the optic foramen, except at 

 its upper and outer part. The External 

 rectus has two heads: the upper one arises 

 from the outer margin of the optic foramen, 

 immediately beneath the Superior rectus ; the 

 lower head, partly from the ligament of Zinn, 

 and partly from a small pointed process of bone 

 on the lower margin of ih& sphenoidal fissure. 

 Each muscle passes forward in the position 

 implied by its name, to be inserted, by a ten- 

 dinous expansion, into the sclerotic coat, about 

 three or four lines from the margin of the 

 cornea. Between the two heads of the External 

 rectus is a narrow interval, through which pass 

 the third, nasal branch of the fifth, and sixth 

 nerves, and the ophthalmic vein. Although 



nearly all these muscles present a common origin, and are inserted in a similar 

 manner in the sclerotic coat, there are certain differences to be observed in them. 

 as regards their length and breadth. The Internal rectus is the broadest : the 

 External, the longest ; and the Superior, the thinnest and narrowest. 



Fig. 150. The relative Position and 

 Attachment of the Muscles of the 

 Left Eyeball. 



Jlectux aperur 



Jjvvat&r 

 Falftb-mSuptnar 



Olliquus Sap friar. 



Jfcffat Inferior 



