136 A MANUAL OF ANATOMY 



rates the orbit from the subjacent antrum of Highmore. It is 

 traversed from behind forwards by the infra-orbital canal, which 

 posteriorly is a groove. At its anterior and inner part is the 

 upper orifice of the lachrymal canal, and external to this is a small 

 depression which gives origin to the inferior oblique muscle of the 

 eyeball. 



The outer wall looks forwards and inwards, and is formed 

 mainly by the orbital surface of the great wing of the sphenoid, 

 and in front of this by a part of the orbital process of the 

 malar. Between the outer wall and the floor is the spheno-maxillary 

 fissure, the front part of which communicates with the zygomatic 

 fossa, and the back part with the spheno-maxillary fossa. Between 

 the outer wall and the roof, towards the posterior part, is the outer 

 portion of the sphenoidal fissure. The part of the orbital process of 

 the malar which forms the front part of this wall presents two 

 foramina (sometimes one) leading to the malar and temporal canals. 



The inner wall is almost vertical, and looks directly outwards. 

 It is formed by four (sometimes five) bones, in the following order 

 from before backwards : (i) the nasal process of the superior 

 maxilla ; (2) the lachrymal ; (3) the os planum or orbital plate of 

 the ethmoid ; and (4) the anterior part of the lateral surface of the 

 body of the sphenoid. If there are five bones, the fifth is a portion 

 of the sphenoidal spongy bone, which would lie behind the os 

 planum of the ethmoid. Between the inner wall and roof, in the 

 ethmo-frontal suture, are the openings of the anterior and posterior 

 ethmoidal or internal orbital canals. At the anterior part of this 

 wall is the lachrymal groove, which lodges the lachrymal sac, and 

 behind this is the lachrymal crest, which gives origin to the tensor 

 tarsi muscle. 



The orbital sutures are as follows : superiorly, the orbito- 

 sphenoidal ; inferiorly, the malo-maxillary and palato-maxillary ; 

 externally, the spheno-malar ; and internally, from before backwards, 

 the lachrymo-maxillary, ethmo-lachrymal, and ethmo-sphenoidal, 

 all of which three are disposed vertically, and ethmo-frontal, which 

 is antero-posterior. 



The orbit has ten (sometimes nine) openings communicating with 

 it. (i) The sphenoidal fissure or foramen lacerum anterius or 

 orbitale, the wide inner end of which forms the apex of the cavity, 

 whilst the narrow outer part lies between the roof and the outer 

 wall. This fissure transmits {a) the third nerve, the sympa- 

 thetic filament to the lenticular ganglion, the fourth, the three 

 branches (frontal, lachrymal, and nasal) of the ophthalmic division 

 of the fifth, and the sixth, cranial nerves ; (b) the superior and in- 

 ferior ophthalmic veins ; (c) the orbital branch of the middle 

 meningeal artery ; and (d) a portion of the dura mater. (2) The 

 optic foramen, situated above and internal to the apex, for the optic 

 nerve and the ophthalmic artery, along with a plexus of sympa- 

 thetic nerve fibres. (3) The supra-orbital notch (or it may be 

 foramen), on the supra-orbital border, for the supra-orbital nerve 



