290 



THE MUSCLES OF THE HEAD AND NECK. 



tween these two origins muscular fibres also spring from a tendinous arch joining 

 the heads over the fissure. The four recti, thus attached posteriorly, pass forwards, 

 one above, one below, and one on each side of the eyeball, becoming flattened as 

 they lie in contact with it, and are inserted by short membranous and slightly 

 expanded tendons into the fore part of the sclerotic coat, at a distance of from three 

 to four lines from the margin of the cornea. 



The external and inferior recti exceed the other two in length. On the other hand, the 

 internal rectus is the broadest and strongest, and the superior the smallest and narrowest of 

 all. At their insertions the internal is nearest to, and the superior is farthest from the edge 

 of the cornea 1 : the internal has the longest, and the external the shortest tendon. Between 

 the heads of the external rectus is a narrow interval which gives passage to the third and 

 sixth nerves and the nasal branch of the fifth nerve, with the ophthalmic veins. 



The superior oblique or trochlearis is a narrow elongated muscle, placed at 

 the upper and inner part of the orbit, internally to the levator palpebrge. It arises 



Fig. 272. A, VIEW OP THE MUSCLES OF THE RIGHT 



ORBIT, FROM THE OUTSIDE, THE OUTER WALL HAVING 



BEEN REMOVED. (Allen Thomson.) \ 



B, EXPLANATORY SKETCH OF THE SAME MUSCLES. 



a, orbital arch ; b, lower margin of tLe orbit ; c, 

 anterior clinoid process ; d, posterior part of the floor 

 of the orbit above the spheno-maxillary fossa ; e, side 

 of the body of the sphenoid bone below the optic fora- 

 men and sphenoidal fissure ; /, maxillary sinus ; 1, 

 levator palpebrse superioris ; 2, pulley and tendon of 

 the superior oblique muscle ; 3, tendon of the superior 

 rectus muscle at its insertion upon the eyeball ; 4, ex- 

 ternal rectus ; 4', in B, tendon of insertion of the same 

 muscle, a large part of which has been removed ; 5, in- 

 ferior oblique muscle crossing the eyeball below the 

 inferior rectus ; 6, inferior rectus ; 7, in B, the internal 

 rectus, and near it, the end of the optic nerve cut short 

 close to the place of its entrance into the eyeball. 



about a line in front of the inner part of the 

 optic foramen ; thence it proceeds towards 

 the front of the orbit, and terminates in a 

 round tendon which passes through a fibro- 

 cartilaginous ring or pulley (trochlea) at- 

 tached to the trocblear fossa of the frontal 

 bone ; it is there reflected outwards, backwards and downwards, and passes between 

 the eye and the superior rectus to be inserted into the sclerotic coat beneath the 

 outer edge of that muscle, and midway between the cornea and the entrance of the 

 optic nerve. 



Relations. This muscle is in contact with the roof of the orbit, the fourth nerve entering 

 its upper surface ; and beneath it lie the nasal nerve, the ophthalmic artery, and the internal 

 rectus muscle. The pulley is lined by a synovial sheath, and from its outer border an invest- 

 ment of firm connective tissue is prolonged on the tendon as far as the eyeball. 



The inferior oblique arises from a minute depression in the orbital plate of 

 the superior maxillary bone, just within the anterior margin of the orbit, and close 

 outside the orifice of the nasal duct. The muscle inclines outwards, backwards and 

 upwards, passing between the inferior rectus and the floor of the orbit, and ends in 

 a tendinous expansion which is inserted, under cover of the external rectus, into the 

 eyeball at its posterior and outer part, and nearer to the optic nerve than the 

 superior oblique. 



1 On the precise mode of insertion of the eye-muscles see E. Fuchs, " Beitrage zur normalcn Anatomic 

 des Augapfels," Arch. f. Ophthalmologie, xxx, 1884. 



