THE REGION OF THE ORBIT. 35 



proceedings connected with them, are better referred to 

 works devoted either to descriptive anatomy or to oph- 

 thalmic surgery, as the limits of the present volume 

 scarcely admit of so special a subject. 



External Orbital Region. 



The external orbital region comprises that of the eye- 

 lids and the lachrymal apparatus. 



The eyelids consist of the following layers : The most 

 external is the skin, which is remarkably thin ; next in 

 order is the subcutaneous cellular tissue, very loose, and 

 destitute of fat, continuous with that of the forehead, 

 and very liable to infiltration, if the effusion of blood 

 takes place beneath the tendon of the occipito-frontalis ; 

 then the orbicularis palpebrarum muscle, separated by 

 the palpebral vessels from the tarsal ligament and car- 

 tilages. The arteries consist of the palpebral branches 

 of the ophthalmic, which anastomose with the facial, 

 temporal, infra-orbital, supra-orbital, and lachrymal. 

 The veins, as a rule, accompany the arteries. The 

 nerves are derived from the facial, the superior maxil- 

 lary of the fifth and the third, which supplies also the 

 levator palpebrse. The next layer is formed of cellular 

 tissue and fat, particularly developed at the margin of 

 the lids, where it is continuous with that of the orbit. 

 The most internal layer is the palpebral conjunctiva, 

 which covers in the Meibomian follicles. The tarsal 

 cartilage of the upper lid is strengthened by the in- 

 sertion into it of the levator palpebrse. The free border 

 of the lids presents the orifices of the Meibomian and 

 ciliary follicles, and their outer margin the cilia. The 

 Meibomian glands are about thirty or forty in number, 



