292 THE MUSCLES AND FASCIJE OF THE HEAD AND NECK. 



they effect without any rotation, their line of action being 1 almost exactly in the horizontal 

 plane of the eyeball. 2nd. It is different with the superior and inferior recti ; for while these 

 muscles undoubtedly are respectively the most direct elevators and depressors of the cornea, 

 they have both a tendency, from the line of their action being to the inner side of the centre 

 of motion of the eyeball, to produce inward direction with a small amount of rotation. This 

 tendency is corrected by the association of the oblique muscles in upward and downward 

 movements ; the inferior oblique being associated with the superior, and the superior oblique 

 with the inferior rectus muscle. The simple action of the superior oblique muscle, when the 

 eye is in the primary position, is to produce a movement of the cornea downwards and 

 outwards, that of the inferior oblique to direct the cornea upwards and outwards, and in both 

 with a certain amount of rotation, though in different directions in the two cases. But these 

 movements caused by the oblique muscles are precisely those which are required to neutralise 

 the inward direction and rotatory movements produced by the superior and inferior recti, and 

 accordingly, by the combined action of the superior rectus and the inferior oblique muscles a 

 straight upward movement is effected, while a similar effect in the downward direction results 

 from the combined action of the inferior rectus and superior oblique muscles. 



It has been farther shown that in all the oblique movements of direction a combination 

 takes place of the action of the oblique with that of the straight muscles. Here, however, 

 two recti muscles are in action and are associated with one oblique muscle, as, for example, 

 in the upward and inward direction, the superior and internal recti with the inferior oblique, 

 and in the downward and inward direction the inferior and internal recti with the superior 

 oblique. And the same is true of the upward and outward and downward and outward 

 movements of direction, for in all these movements the action of the oblique muscles is 

 necessary to control or supplement the rotatory tendency of the recti muscles. 



It is also obvious that the effect of the contraction of each muscle will vary according to 

 the position of the eyeball. Thus, if the eye be abducted, so that the transverse axis of the 

 ball coincides with the axis of movement of the superior and inferior recti, these muscles 

 will simply elevate or depress the cornea without rotation ; whereas if the eye be adducted 

 the rotatory tendency of the same muscles is increased, and requires a stronger effort on the 

 part of the associated obliqui for its correction ; and in extreme adduction the eyeball is 

 elevated and depressed mainly by the inferior and superior oblique muscles, which have in 

 great measure lost their rotatory action. 



The ocular movements are always bilateral ; but while in the upward and downward move- 

 ments both eyes are always turned in the same direction, in the lateral movements the two 

 eyes may either be directed to the same side, the one being abducted and the other adducted, or 

 they may both be adducted so as to bring about the convergence of the visual axes necessary 

 for near vision. 



(For fuller information as to the movements of the eyes the reader is referred to treatises 

 on Physiology, as well as to the following special works :' Donders, " On the Anomalies of 

 Accommodation," &c., Syd. Soc., 1864 ; Helmholz, Proc. Roy. Soc..xiii, 186, and ''Physiological 

 Optics," and Bering in Hermann's " Handbuch der Physiologic," Bd. iii.) 



Fasciee of the orbit. The space within the orbit which is not occupied by the eyeball 

 and its muscles, or other parts belonging to it, is completely filled with soft fat and delicate 

 yielding connective tissue. In various places this last is condensed into layers of slender 

 fascia of various degrees of strength, the principal of which is that known as the fascia or 

 capsule of Tenon, a thin membrane surrounding the greater part of the eyeball, and forming 

 the wall of a socket in which the globe plays. The fascia is perforated behind by the optic 

 nerve and the ciliary vessels and nerves, there becoming continuous with the connective 

 tissue investing those structures, and in front it extends nearly as far as the cornea, where it 

 ends by being attached to the ocular conjunctiva. Its inner surface is connected to the 

 sclerotic coat of the eye only by delicate bundles of yielding connective tissue, the two being 

 separated for the most part by an extensive lymph-space, so that it seems to serve all the 

 purposes of a synovial membrane in the movements of the globe. The fascia is also pierced 

 by the muscles of the eyeball near their insertions, and it sends a tubular prolongation on 

 each of these, which speedily degenerates, however, into a simple areolar investment, except 

 in the case of the sheath on the tendon of the superior oblique, which is stronger than the 

 others and is continued as far as the pulley. The sheaths of the recti adhere closely to the 

 muscular substance, and from their outer part expansions are given off to the margin of the 

 orbit, which serve to limit the degree of contraction of the muscles. The processes from the 

 sheaths of the inner and outer recti are stronger than the other two, especially the external, 

 which is attached to the malar bone and external tarsal ligament. The inner expansion is 

 similarly fixed to the crest of the lachrymal bone and the reflected portion of the internal 

 tarsal ligament. The offset from the sheath of the superior rectus is connected with the 

 tendon of the levator palpebrse (p. 289), and from that of the inferior rectus fibres are 

 continued forwards into the lower tarsal plate ; these muscles are thus enabled to exercise an 

 influence upon the eyelids. Lockwood describes under the name of the suspensory ligament of 

 the eye a boat-shaped thickening of the lower part of the capsule, which is attached at each 



