398 NERVOUS SYSTEM. 



pendencies or Auxiliary parts, all of which are situated within 

 the orbit, and fill up its cavity. 



SECT. I. OF THE AUXILIARY PARTS OF THE EYE. 



The Eyelids (Palpebras) are placed at the anterior orifice of 

 the orbit, and serve to shut out the light from the eye, by their 

 closing; and also, by their'frequent motions, to sweep the front 

 of the eyeball, so as to remove, from its transparent part, moats 

 and dust. They are distinguished into upper and lower, and 

 the place at each end, where the horizontal fissure between them 

 ceases, is called their Commissure, Angle or Canthus. The 

 angle next to the nose, or the internal, is called the Great one, 

 and the other, the Little one. 



The Internal Canthus is united to the nasal process of the su- 

 perior maxillary bone by a rounded tendon, (Ligamentum Pal- 

 pebrale Jnternum,) the origin of the orbicularis palpebrarum mus- 

 cle, and which passes horizontally inwards, being nearly half 

 an inch in length. It throws the skin into a small ridge, which 

 may be distinctly seen and felt at this point. The External 

 Canthus is held in place by its general attachments of cellular 

 substance and by the external palpebral ligament. 



The upper eyelid is somewhat larger than the lower, but the 

 structure of both is the same, for each one is formed by skin ex- 

 ternally ; next to it a plane of muscular fibres, being the orbi- 

 cularis palpebrarum; then a plate of cartilage; and, lastly, a 

 thin membrane uniting it to the eyeball. 



There is nothing ia the texture of the skin of the eyelid which 

 needs description in a manner more particular than that of 

 stating its fineness, its thinness, the looseness of its attachment 

 to the muscle beneath by long yielding cellular substance, and 

 the deficiency of adipose matter. It is rendered prominent at 

 the superior margin of the orbit, both by the projection of the 

 bone there, and by the presence of the corrugator supercilii 

 muscle at its internal extremity. This prominence is furnished 

 with an arched cluster of hairs, (Supercilia,) which have their 

 loose ends inclined horizontally outwards, and are rather more 

 abundant at the root of the nose than externally. The super- 

 cilia of the two sides are separated commonly by a small bare 



