A'TION OF THE OBLIQUE MUSCLKs. 651 



therefore cause the front of the eye to be directed downwards and 

 outwards. The inferior oblique would similarly turn the front of 

 the eye upwards and outwards. In consequence of their transverse 

 direction, these muscles would also tend to rotate the eyeball around 

 its antero-posterior axis, the superior oblique depressing, and the 

 inferior oblique elevating the inner end of the horizontal meridian 

 of the eye, but movements of this nature take place only to a very- 

 limited extent during life. 



The oblique muscles are believed to act mainly in controlling the and with 



tendency of the superior and inferior recti to rotate the eyeball and su P eri r . 



. . , JL ,. anf inferior 



turn it inwards. Ihus, to move the eye directly upwards, the superior lecti. 



rectus and the inferior oblique are used, while the inferior rectus and 

 superior oblique co-operate in directing the eye downwards. 



Dissection. To expose the small tensor tarsi muscle, the remain- Seek tensor 

 ing portion of the palpebral fascia is to be separated from the margin arsu 

 of the orbit ; but the lids must be left attached at the inner side by 

 means of the internal tarsal ligament. On clearing away a little 

 areolar tissue in the neighbourhood of the inner commissure, after 

 the lids have been placed across the nose, the pale fibres of the 

 tensor tarsi will be seen. 



The TENSOR TARSI MUSCLE arises from the crest of the lachrymal Tensor tarsi 

 bone, and slightly from the bone behind the crest. Its fibres are m ' 

 pale, and form a very small flat band, behind the internal tarsal 

 ligament, which divides like that structure into a slip for each eye- 

 lid. In the lid the slip lies by the side of the lachrymal canal, and insertion ; 

 blends with the fibres of the orbicularis along the free margin of the 

 tarsus. 



Action. The tensor tarsi draws backwards the inner canthus of use. 

 the eye and compresses the lachrymal sac, after it has been dilated 

 by the orbicularis palpebrarum in the act of winking. 



Dissection. A small nerve, the orbital branch of the superior Trace offset 

 maxillary trunk, lies along the lower part of the outer wall of the maxillary"" 

 orbit, and is now to be brought into view by the removal of the eye- nerve - 

 bull ami its muscles. This nerve is very soft and easily broken, 

 and is covered, as it enters the orbit through the spheno-maxillary 

 fissure, by pale fleshy fibres (orbitalis muscle). Two branches, 

 temporal and malar, are to be traced forwards from it ; and the 

 junction of a filament of the lachrymal nerve with the former is to 

 be sought close to the bone. The outer wall of the orbit may be 

 cut away bit by bit, to follow the temporal branch to the surface 

 of the head. 



The TEMPORO-MALAR or ORBITAL BRANCH of the superior maxillary Orbital 

 nerve arises in the spheno-maxillary fossa, and divides at the back JjJJJJi^' 

 of the orbit into malar and temporal branches, which ramify on the maxillary 

 face and the side of the head with companion vessels. 



The malar branch is directed forwards through the canal of the its malar 

 same name in the malar bone to supply the skin of the upper and 

 outer part of the cheek, where it communicates with the malar 

 branches of the facial nerve. 



