162 OSTEOLOGY. 



frontal and the upper margin of the orbital surface of the great wing of the 

 sphenoid, lateral to which the zygomatic process of the frontal articulates with the 

 zygomatic bone, often forming a ridge which limits the fossa for the lodgment of 

 the lacrimal gland inferiorly (Whitnall). Medially the roof is marked off from the 

 medial wall by a suture, more or less horizontal in direction, between the orbital 

 plate of the frontal and the following bones, in order from before backwards, viz., 

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

 the ethmoid. In the suture between the last-mentioned bone and the frontal 

 there are two foramina, the anterior and posterior ethmoidal foramina ; both trans- 

 mit ethinoidal vessels and the ethmoidal branches of the naso-ciliary nerve as 

 well. The roof is concave from side to side, and to some extent also from before 

 backwards. About midway between the fronto-maxillary suture and the supra- 

 orbital notch or foramen, but within the margin of the orbit, there is a small 

 depression, occasionally associated with a spine (fovea vel spina trochlearis), for the 

 attachment of the cartilaginous pulley of the superior oblique muscle of the 

 eyeball. Under cover of the zygomatic process the roof is more deeply exca- 

 vated, forming a shallow fossa for the lodgment of the lacrimal gland (fossa 

 glandulae lacrimalis). In front, the roof separates the orbit from the frontal sinus, 

 and along its medial border it is in relation with the ethmoidal air-cells. The 

 relation to these air spaces is variable, depending on the development and size of 

 the sinuses. The rest of the roof, which is very thin, forms by its upper surface 

 part of the floor of the anterior cranial fossa, in which are lodged the frontal 

 lobes of the cerebrum. 



The floor of the orbit is formed by the orbital surface of the maxilla, together 

 with part of the orbital surface of the zygomatic bone, and a small triangular 

 piece of bone, the orbital process of the palate, which is wedged in posteriorly. 

 Laterally, for three-quarters of its length posteriorly, it is separated from the lateral 

 wall, which is here formed by the great wing of the sphenoid, by a cleft called the 

 inferior orbital fissure. Through this there pass the maxillary division of the 

 trigeminal nerve on its way to the infra-orbital canal, the zygomatic branch of 

 the maxillary nerve, the infra-orbital vessels, a branch connecting the inferior 

 ophthalmic vein with the pterygoid plexus, and some twigs from the spheno- 

 palatine ganglion. By means of this fissure the orbit communicates with the 

 ptery go -palatine fossa behind, and the infra - temporal fossa to the lateral side, 

 though in the recent condition the fissure is bridged over by the involuntary 

 orbitalis muscle of Muller. Medially the floor is limited from behind forwards 

 by the suture between the following bones, viz., the orbital process of the palate 

 below with the body of the sphenoid above and behind, and the lamina papyracea 

 of the ethmoid above and in front anterior to which the orbital surface of the 

 maxilla below articulates with the lamina papyracea of the ethmoid and the 

 lacrimal above and in front. At the anterior extremity of this line of sutures 

 the medial edge of the orbital plate of the maxilla is notched and free between 

 the point where it articulates with the lacrimal posteriorly and the part from 

 which its frontal process arises. Here it forms the lateral edge of a canal, down 

 which the membranous naso-lacrimal duct passes to the nose. The floor of the 

 orbit is thin behind and at the sides, but thicker in front, where it blends with 

 the orbital margin. Passing in a sagittal direction through its substance is the 

 infra-orbital canal, the roof of which is usually deficient behind, where it becomes 

 continuous with a broad, shallow groove, which leads forwards from the anterior 

 margin of the inferior orbital ' fissure. This canal (canalis infraorbitalis) opens on 

 the anterior surface of the maxilla immediately below the orbital margin (foramen 

 infraorbitale) and transmits the maxillary division of the trigeminal nerve, together 

 with the infra-orbital vessels. The floor forms a thin partition which separates the 

 orbit from the maxillary sinus, which lies beneath it. Medially it completes the 

 lower ethmoidal air-cells, and separates the orbit from the middle meatus of the 

 nasal cavity. 



The lateral wall of the orbit, which is the strongest, is formed by the orbital 

 surface of the great wing of the sphenoid and the superior part of the orbital surface 

 of the zygomatic bone. Above it, behind, is the superior orbital fissure, whilst below, 



