370 



THE MUSCLES AND FASCIA 



Rectus superior. 

 Levator 



superior. 

 superior obiique 



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

 osteum of the orbit and lacrimal gland; and, in the lid, with the inner surface of the tarsal liga- 

 ment; by its ocular surface, with the Superior rectus, and, in the lid, with the conjunctiva. A 

 small branch of the oculomotor nerve enters its under surface. 



The four Recti (Fig. 293) arise from a fibrous ring (annulus tendineus communis) 

 which surrounds the upper, inner, and lower margins of the optic foramen and 

 encircles the optic nerve. Two specialized parts may be made out: (1) A 

 lower, the tendon or ligament of Zinn, which gives origin to the Inferior rectus, 

 part of the Internal rectus, and the lower head of the External rectus; and (2) 

 an upper, the superior tendon of Lockwood, which gives origin to the Superior rectus, 

 the rest of the Internal rectus, and the upper head of the External rectus. 



Each of the four Recti passes forward in the position implied by its name, to 

 be inserted by a tendinous expansion into the sclera, about a quarter of an inch 

 from the margin of the cornea. Between the two heads of the External rectus 



is a narrow interval, through which pass the 

 two divisions of the oculomotor nerve, the nasal 



, , i , i i i i>i 



branch or the ophthalmic division or the tn- 



. 111 



gemmal nerve, the abducent nerve, and the 

 ophthalmic vein. Of the four Recti, the 

 Internal rectus j s tne broadest, the External 

 the longest, and the Superior the thinnest and 

 narrowest. 



The Superior oblique (TO. obliquus oculi 

 superior] is a fusiform muscle placed at the 

 upper and inner side of the orbit, internal 

 to the Levator paipebrae. It arises a litttle 



. , . -PI p 



above the inner margin or the optic foramen 

 (Fig. 293), and, passing forward to the inner 



angle of the orbit, terminates in a rounded tendon, which plays in a fibrocarti- 

 laginous ring or pulley, the trochlea (trochlea TO. obliqui oculi superioris), attached 

 to the trochlear fossa near the internal angular process of the frontal bone. The 

 contiguous surfaces of the tendon and ring are lined with a delicate synovial 

 membrane and are enclosed in a thin fibrous investment. The tendon is reflected 

 backward, outward, and downward beneath the Superior rectus to the outer part 

 of the globe of the eye, and is inserted into the sclera, behind the equator of the 

 eyeball, the insertion of the muscle lying between the Superior and External recti. 



Relations. By its orbital surface, with the periosteum covering the roof of the orbit and the 

 trochlear nerve; the tendon, where it lies on the globe of the eye, is covered by the Superior 

 rectus ; by its ocular surface, with the nasal nerve, ethmoidal arteries, and the upper border of the 

 Internal rectus. 



The Inferior oblique (TO. obliquus oculi inferior) is a thin, narrow muscle placed 

 near the anterior margin of the orbit. It arises from a depression on the orbital 

 plate of the maxilla, external to the lacrimal groove (Fig. 292). Passing outward, 

 backward, and upward between the Inferior rectus and the floor of the orbit, 

 and then between the eyeball and the External rectus, it is inserted into the outer 

 part of the sclera between the Superior and External recti, near to, but somewhat 

 behind, the tendon of insertion of the Superior oblique. Beyond its insertion 

 a thin layer of non-striated muscle fibres (inferior tarsal muscle) continues into 

 the lower eyelid to be inserted into the inferior tarsal plate. 



Relations. By its ocular surface, with the globe of the eye and with the Inferior rectus; by 

 its orbital surface, with the periosteum covering the floor of the orbit, and with the External 

 rectus. Its borders look forward and backward; the posterior one receives a branch of the 

 motor oculi nerve. 



s upper head, 

 Lower head - 



FIG. 293. The relative position and attach- 



ment of the muscles of the left eyeball. 



