DISSECTION OF THE HEAD AND NECK. 211 



antero-posterior horizontal axis, the superior muscle elevating the nasal 

 angle of the pupil, while the inferior muscle depresses it. The retractor 

 oculi pulls the eyeball directly backwards into its cavity, and is thus, by 

 pressure exerted on the orbital fat, instrumental in protruding the mem- 

 brana nictitans, as explained at page 173. 



The Ophthalmic Artery is a branch of the internal maxillary, from 

 which it is detached within the subsphenoidal canal. Emei-ging from 

 that canal at the back of the orbit, it is directed inwards to enter the 

 internal orbital foramen ; and in this course it passes between the 

 superior rectus and the retractor oculi, where the latter surrounds the 

 optic nerve. By the internal orbital foramen it reaches the forepart of 

 the cranial cavity. It is further described at page 238. In the 

 orbital part of its course it gives off the following branches : — 



1. The Sujiraorhital Artery ascends on the inner Avail of the orbit to 

 pass through the foramen of the same name. 



2. The Lachrymal Artery, distributed to the gland and the upper 

 eyelid. 



3; Muscular Branches. 



4. Ciliary Branches to the eyeball. 



5. The Central Artery of the Retina, which places itself in the axis of 

 the optic nerve, and enters the eyeball. 



The Orbital Branch of the superior dental artery. This is a long 

 and slender branch detached from the parent vessel before it enters the 

 superior dental canal. It creeps over the floor of the orbit to reach the 

 face, where it anastomoses with the submaxillary artery (Plate 29). 



Veins. The structures within the orbit are drained by vessels which 

 unite to form the ophthalmic vein. This, after uniting with the alveolar 

 vein, passes into the cranial cavity by the foramen lacerum orbitale. 



The Ophthalmic Nerve is one of the three primary divisions of the 

 5th nerve. It is a sensory nerve, and divides into the following three 

 branches, which issue in company from the foramen lacerum orbitale : — 



1. The Siipraorhital Nerve, accompanying the artery of the same 

 name. 



2. The Lachrymal Nerve, to the gland, and giving off a branch which 

 traverses the ocular sheath to reach the skin over the temporal fossa. 



3. The Palx)ehro-nasal Nerve divides into a nasal branch which 

 accompanies the ophthalmic artery through the internal orbital foramen, 

 and a palpebral branch to the lower eyelid and inner canthus. The 

 palpebro-nasal nerve also furnishes the sensory filaments to the ciliary 

 ganglion, through which it supplies sensory fibres to the eyeball. 



The Orbital Branch of the superior maxillary division of the 5th 

 nerve issues with the parent nerve from the foramen rotundum. It 

 passes at the outer side of the ocular sheath to gain the temporal can- 

 thus of the eyelids, where it is distributed. It is sensory. 



