28 OUTLINES OF EQUINE ANATOMY. 



part of the rim of the orbit, its root becomes expanded in 

 becoming attached to the outer edge of the facial plate, 

 and presents the supra-orbital foramen. The anterior part 

 of this edge forms the inner part of the rim of the orbit, 

 and is continuous downwards with the orbital plate. The 

 anterior margin presents a laminated squamous surface to 

 the outer part of which the lachrymal, to the inner the 

 nasal bone becomes attached. The inner margin presents 

 a roughened edge for apposition with its fellow, from the 

 anterior part of which a thin plate of bone is reflected 

 downwards to form the inner boundary of the frontal sinus 

 lying in contact with its fellow. The posterior boundary is 

 squamous, most so on the outer side, for articulation with 

 the parietal bone. The cranial plate blends superiorly 

 with the posterior part of the under surface of the facial 

 plate, and presents digital depression for the cerebral 

 convolutions. Its inner margin is serrated and lies in 

 contact with its fellow. Its inferior margin joins the 

 upper part of the crista galli and cribriform plates of the 

 ethmoid. Its outer margin joins the orbital plate. The 

 anterior surface helps to form the frontal sinus, and from 

 the inner margin of the surface runs the vertical bony 

 septum which inf eriorly is reflected to form a narrow ledge 

 of bone running obliquely forwards and upwards in 

 blending anteriorly with the facial plate in a sharp point. 

 The orbital plate externally is concave, forming the inner 

 part of the orbit. Near the root of the orbital process it 

 presents the iibro-cartilaginous loop through which the 

 superior oblique muscle of the eye plays. Posteriorly it is 

 continued below the orbital j^rocess, helping to form the 

 temporal fossa, and articulating with the squamous tem- 

 poral bone. This plate presents a deep indentation, in- 

 feriorly extending upwards towards the orbital loop. It 

 terminates in a point, and accommodates the orbital surface 

 of OS ethmoides, which, by the older anatomists, was 

 termed os planum. The anterior margin inferiorly gives 

 attachment to os palati ; centrally to the superior maxil- 

 lary bone ; superiorly to the lachrymal bone. The inner 

 surface of this plate posteriorly is separated by a remark- 

 able groove from the cranial surface, and has a squamous 

 suture with the ala of the ethmoid ; centrally it gives attach- 

 ment to the cranial plate ; anteriorly forms the convex outer 

 wall of the frontal sinus. At the extreme postero-inferior 



