CAVITY <>!' Tin: 



L037 



Two of those axes arc horizontal and one vertical; they all pass through the centre 

 of rotation at right angles ID one another. Hy rotation of the eye on its vertical 

 axis I lie cornea is moved outwards (towards the temple) and inwards (towards the 

 |; movements called respectively abduction and adduction. In upward and 

 downward movements of the cornea the eye rotates on its horizontal equatorial 

 axis. The other principal axis of rolat:<>ii is the sagil tal, which \\e have previously 

 described as corresponding to the line joining the anterior and posterior poles of the 

 globe (page H)iM). In rotation of the eye on its sagittal axis, therefore, the cornea 

 may l>e said to move as a wheel on its axle, for its centre now corresponds to one 

 end of the axis; in other words, this is a rotation of the cornea. Such nioven .. 

 may, consequently, be expressed with reference to their etTeci on an imaginary 

 spoke of the corneal wheel e. g., one running vertically upwards from the corneal 

 centre. Thus wo may say 'rotation of the cornea outwards' when this part of the 



MO outer canthus. or ' inwards' when towards the nose. 



The only two muscles that rotate the eyeball merely on one axis are the ex- 

 ternal rectus and the internal rectus; the former abducting, and the latter ad- 

 ducting, the cornea. The action of the superior and inferior recti is complicated by 

 the obliquity of the axes of muscles aid globe previously mentioned. 



Fio. 736. VIEW OF \FIOVE, SHOWING THE ()<TLAK MTSCLES. 



(From Hirschfeld and Leveilld.) 



Internal rectus muscle 



Superior oblique muscle 



Troohlea 



Levator palpebrao superiorly 

 muscle, cut 



External rectus muscle 

 Inferior oblique muscle 

 Superior rectus muscle 



Levator palpcbrfle superiorly 

 muscle, out 



The chief action of the superior rectus is to draw the cornea upwards, but at 

 the same time it adduuts and rotates the cornea inwards. 



The inferior rectus mainly draws the cornea downwards, also adducting it and 

 rotating it outwards. 



The chief action of the superior oblique is to rotate the cornea inwards, also 

 drawing it downwards and slightly abducting it. 



The inferior oblique mainly rotates 'the cornea outwards, also drawing it up- 

 wards and slightly abduct in 



The fasciae of the orbit. The orbital contents are bound together and sup- 

 ported by fibrous tissues, \\hicli are connected with each other, but which may 

 conveniently be regarded as belonging to three systems. These are: (1) Tints- 

 lining the bony walls; (_>") thos" ensheathing the muscles; and (3) the tissue which 

 partially encapsules the eyeball. 



1. The orbital periosteum, or periorbita, is closely applied to the bones form- 

 ing the walls of the cavity, but may be stripped off with comparative ease. It 

 presents openings for the passage of vessels and nerves entering and leaving the 

 orbit. Posteriorly this tissue is very firm, being joined by p of the dura 



mater at the optic canal and superior orbital fissure; at the optic foramen* it is al-o 



