THE FKONT OF THE SKULL. 163 



and extending much farther forward, is the inferior orbital fissure. The posterior 

 portion of this wall, formed by the great wing of the sphenoid, serves as a partition 

 between the orbit and the anterior extremity of the middle cranial fossa, in which 

 is lodged the pole of the temporal lobe of the cerebrum. In front of this, and 

 behind the line of the spheno-zygomatic suture, this wall is strengthened on its 

 outer aspect by its confluence with the cranial wall. Still more anteriorly, the 

 lateral wall separates the orbit from the temporal fossa. The anterior margin 

 of the lateral wall is stout and formed by the zygomatic bone, behind which, 

 formed in part by the orbital process of the zygomatic bone and the zygomatic 

 edge of the great wing of the sphenoid, it forms a fairly thick partition between 

 the orbit in front and the temporal fossa behind. Crossing this surface from 

 above downwards, close to the anterior extremity of the inferior orbital fissure, 

 is the suture between the zygomatic bone and the great wing of the sphenoid 

 (sutura sphenozygomatica). This wall is pierced in front by one or two small 

 canals (foramina zygomatico-orbitalia), which traverse the zygomatic bone and 

 allow the transmission of the zygoniatico- temporal and zygomatico-facial branches 

 of the zygomatic portion of the maxillary division of the trigeminal nerve. A 

 small tubercle, which can be more readily felt than seen, is situated just within 

 the orbital margin near the middle of the anterior part of this wall, and indicates 

 the site of attachment of the lateral palpebral raphe (Whitnall). 



The medial wall of the orbit is formed from before backwards by a small part 

 of the frontal process of the maxilla, by the lacrimal, and by the lamina papyracea 

 of the ethmoid, posterior to which is a small part of the lateral aspect of the 

 body of the sphenoid in front of the optic foramen. Above, the orbital part of 

 the frontal bone forms a continuous suture from before backwards with the bones 

 just enumerated; whilst below, the lacrimal and the lamina papyracea of the 

 ethmoid articulate with the orbital plate of the maxilla ; posteriorly the posterior 

 extremity of the lamina papyracea and the anterior part of the body of the sphenoid 

 articulate with the orbital process of the palate. The orbital surface of the 

 lacrimal bone is divided into two by a vertical ridge the lacrimal crest (crista 

 lacrimalis posterior) which forms in front the posterior half of a hollow, the 

 fossa sacci lacrimalis, the anterior part of which is completed by the channelled 

 posterior border of the frontal process of the maxilla. In the fossa is lodged the 

 lacrimal sac, whilst passing from it and occupying the canal, of which the upper 

 opening is at present seen, is the membranous naso- lacrimal duct. The lower 

 part of the fossa separates the orbit from the anterior part of the middle meatus 

 of the nasal cavity. To the medial side of the upper part of the fossa for the 

 lacrimal sac lie the anterior ethmoidal cells, the passage leading from the nose to 

 the frontal sinus (infundibulum ethmoidale), and the part of the bone behind the 

 lacrimal crest forms the thin partition between the orbit and the ethmoidal cells. 

 Behind, where the body of the sphenoid forms part of the medial wall of the orbit, 

 the sphenoidal air sinus is in relation to the apex of that space, though here the 

 partition wall between the two cavities is much thicker. 



The skeleton of the face on its anterior surface is formed by the two maxillae, 

 the frontal processes of which have been already seen to pass up to articulate 

 with the medial angular processes of the frontal bone, thus forming the lower 

 halves of the medial margins of the orbits. Joined to the maxillae laterally are 

 the zygomatic bones, which are supported by their union with the temporal 

 bones posteriorly through the medium of the zygomatic arches. The suture 

 which separates the zygomatic from the maxilla (sutura zygomaticomaxillaris) 

 commences above about the centre of the inferior orbital margin and passes 

 obliquely downward and laterally, its inferior end lying in vertical line with 

 the lateral orbital margin. The two maxillae are separated by the nasal cavities, 

 which here open anteriorly. Above, the two nasal bones are wedged in between 

 the frontal processes of the maxillae ; whilst below the apertura piriformis, the 

 maxillae themselves are united, in the middle line by the intermaxillary suture 

 (sutura intermaxillaris). 



The apertura piriformis (piriform aperture) (O.T. nasal aperture or 

 anterior nares), which lies below and in part between the orbits, is of variable 



11 a 



