SUPERIOR OBLIQUE MUSCLE. 53 



Occasionally it has a communicating filament behind with the fourth 

 nerve. 



The nasal nerve is not visible at this stage of the dissection : it will be 

 noticed afterwards at p. 43. 



Dissection. Divide the frontal nerve about its middle, and throw the 

 ends forwards and backwards : by raising the posterior part of the nerve, 

 the separate origin of the nasal branch from the ophthalmic trunk will 

 appear. The lachrymal nerve may remain uncut. 



The LEVATOR PALPEBR^E SUPERIORIS (fig. 10, B) is the most superfi- 

 cial muscle, and is attached posteriorly to the roof of the orbit in front of 

 the optic foramen. The muscle widens in front, and bends downwards in 

 the eyelid to be inserted by a wide tendon into the fore part of the tarsal 

 cartilage. 



By one surface the muscle is in contact with the frontal nerve and the 

 periosteum ; and by the other, with the superior rectus muscle. If it is 

 cut across about the centre a small branch of the third nerve will be seen 

 entering the posterior half at the under surface. 



Action. The lid-cartilage is made to glide upwards over the ball by this 

 muscle, so that the upper edge is directed back and the lower forwards, 

 the teguments of the lid being bent inwards at the same time. If the eye- 

 ball is directed down, the movement of the lid is less free, because the 

 conjunctiva is put on the stretch. 



The RECTUS SUPERIOR (fig. 10, D ) is the upper of four muscles that lie 

 arouud the globe of the eye. It arises from the upper part of the optic 

 foramen, and is connected with the other recti muscles around the optic 

 nerve. In front the fleshy fibres end in a tendon, which is inserted, like 

 the other recti, into the sclerotic coat of the eyeball about a quarter of an 

 inch behind the transparent cornea. 



The under surface of the muscle is in contact with the globe of the eye, 

 and with some vessels and nerves to be afterwards seen ; the other surface 

 is covered by the preceding muscle. The action of the muscle will be 

 given with the other recti (p. 57). 



The SUPERIOR OBLIQUE MUSCLE (fig. 10, A ) is thin and narrow, and 

 passes through a fibrous loop at the inner angle of the orbit before reach- 

 ing the eyeball. The muscle arises behind from the inner part of the 

 optic foramen, and ends anteriorly in a rounded tendon, which, after pass- 

 ing through the loop before referred to (fig. 11) is reflected backwards and 

 outwards between the superior rectus and the globe of the eye, and is in- 

 serted into the sclerotic coat behind the middle of the ball. 



The fourth nerve is supplied to the orbital surface of the muscle, and 

 the nasal nerve lies below it. The thin insertion of the muscle lies between 

 the superior and the external rectus, and near the tendon of the inferior 

 oblique. 



The pulley, or trochlea (fig. 11), is a fibro-cartilaginous ring nearly a 

 quarter of an inch wide, which is attached by fibrous tissue to the depres- 

 sion of the frontal bone at the inner angle of the orbit. A fibrous layer is 

 prolonged from the margins of the pulley on the tendon ; and a synovial 

 membrane lines the ring, to facilitate the movement of the tendon through 

 it. To see the synovial membrane and the motion of the tendon, this pro- 

 longation must be cut away. 



For the use of the muscle, see the description of the inferior oblique, 

 p. 59. 



