178 OBLIQUUS INFERIOR. 



the origin of the superior rectus from the margin of the optic foramen ; 

 the nasal, third and sixth nerves passing between its heads. It is inserted 

 into the outer surface of the globe of the eye at a little more than two lines 

 from the margin of the cornea. 



Relations. By its internal surface with the third, the nasal, the sixth, 

 and the optic nerve, the ciliary ganglion and nerves, the ophthalmic artery 

 and vein, the adipose tissue of the orbit, the inferior oblique muscle and 

 the eyeball. By its external surface with the periosteum of the orbit ; and 

 by the upper border with the lachrymal vessels and nerve and the lachry- 

 mal gland. 



The recti muscles present several characters which are common to all ; 

 thus they are thin, have each the form of an isosceles triangle, bear the 

 same relation to the globe of the eye, and are inserted in a similar manner 

 into the sclerotica, at about two lines from the circumference of the cornea. 

 The points of difference relate to thickness and length ; the internal rectus 

 is the thickest and shortest, the external rectus the longest of the four, and 

 the superior rectus the most thin. The insertion of the four recti muscles 

 into the globe of the eye forms a tendinous expansion, which is continued 

 as far as the margin of the cornea, and is called the tunica albuginea. 



The OBLIQUUS SUPERIOR (trochlearis) is a fusiform muscle arising from 

 the margin of the optic foramen, and from the fibrous sheath of the optic 

 nerve ; it passes forwards to the pulley beneath the internal angular pro- 

 cess of the frontal bone ; its tendon is then reflected beneath the superior 

 rectus muscle, to the outer and posterior part of the globe of the eye, 

 where it is inserted into the sclerotic coat, near the entrance of the optic 

 nerve. The tendon is surrounded by a synovial membrane, while passing 

 through the cartilaginous pulley. 



Relations. By its superior surface with the fourth nerve, the supra- 

 trochlear nerve, and with the periosteum of the orbit. By the inferior 

 surface with the adipose tissue of the orbit, the upper border of the inter- 

 nal rectus and the vessels and nerves in relation with that border. 



The OBLIQUUS INFERIOR, a thin and narrow muscle, arises from the 

 inner margin of the superior maxillary bone, immediately external to the 

 lachrymal groove, and passes beneath the inferior rectus, to be inserted 

 into the outer and posterior part of the eyeball, at about two lines from 

 the entrance of the optic nerve. 



Relations. By its superior surface with the inferior rectus muscle and 

 with the eyeball ; and by the inferior surface with the periosteum of the 

 floor of the orbit, and the external rectus muscle. 



According to Mr. Farrall* the muscles of the orbit are separated from 

 the globe of the eyeball and from the structures immediately surrounding 

 the optic nerve, by a distinct fascia, which is continuous with the broad 

 tarsal ligament and with the tarsal cartilages. This fascia the author terms 

 the tunica vaginalis oculi^ it is pierced anteriorly for the passage of the 

 six orbital muscles, by six openings through which the tendons of the 

 muscles play as through pulleys. The use assigned to it by Mr. Farrall 

 is to protect the eyeball from the pressure of its muscles during their ac- 

 tion. By means of this structure the recti muscles are enabled to impress 



In a paper read before the Royal Society, on the 10th of June, 1841. 

 t This fascia was first described by Mr. JDalrymple in his work on the "Anatomy ol 

 the Human Eye." 1834. 



