52 



DISSECTION OF THE ORBIT. 



former passes into the orbit between the heads of the external rectus, but 

 the other two lie, as before said, above the muscles. 



The frontal nerve (fig. 10, 2 ) is close to the outer side of the fourth as 

 it enters the orbit, and is much larger than the lachrymal branch. In its 

 course to the forehead the nerve lies along the middle of the orbit, and 

 supplying anteriorly a supra-trochlear brancli ( 4 ), leaves that cavity by 

 the supra-orbital notch. Taking the name supra-orbital, it ascends on 

 the forehead, and supplies the external part of the head (p. 21). 



Fig. 10. 



Muscles : 



a Superior oblique. 

 6. Levator palpebrse. 



c. External rectus. 



d. Superior rectus. 

 /. Lachrymal gland. 



Nerves : 





1. Fourth. 



2. Frontal. 



3. Lachrymal. 



4. Supra-trochlear. 



6. Offset of lachrymal to join tera- 

 poro-malar. 



FIRST VIEW OF THE ORBIT (Illustrations of Dissections). 



Whilst in the notch the nerve gives palpebral filaments to the upper lid. 



The supra-trochlear branch ( 4 ) passes inwards above the pulley of the 

 upper oblique muscle, and leaves the orbit to end in the eyelid and fore- 

 head (p. 23). Before the nerve turns round the margin of the frontal bone, 

 it sends downwards a branch of communication to the infra-trochlear 

 branch of the nasal nerve. Frequently there are two supra-trochlear 

 branches ; in such instances one arises near the back of the orbit. 



The lachrymal nerve (fig. 10, 3 ) after entering the orbit in a separate 

 tube of the dura mater, is directed forwards in the outer part of the cavity, 

 arid beneath the lachrymal gland to the upper eyelid, where it pierces the 

 palpebral ligament, and is distributed to the structure of the lid. 



The nerve furnishes branches to the lachrymal gland ; and near the 

 gland it sends downwards one or two small filaments ( 6 ) to communicate 

 with the temporo-malar or orbital branch of the superior maxillary nerve. 



