OSTEOLOGY. 



27 



part of tlie crest of tlie occiput towards tlie orbital process 

 of the frontal bone, and whicb gives attachment to auri- 

 cular muscles. The outer division helps to form the 

 temporal fossa, and affords attachment to temporalis ; it is 

 continued by a thin, very rough squamous surface, on 

 which the squamous temporal bone rests. The inner 

 portion of the external surface is immediately subcu- 

 taneous. The poster -internal margin articulates by suture 

 with OS triquatrum, the inner margin similarly with its 

 fellow. The anterior margin inwardly presents a rough 

 surface for squamous articulation with os frontis, out- 

 wardly the outer layer of the bone projects, so that \t rests 

 on OS frontis. The external margin forms the thin jagged 

 edge of the squamous suture with the squamous temporal 

 bone, as also does the postero-external margin, which meets 

 with the postero -internal, forming a point which articulates 

 with OS occipitis. The inner surface of the bone is mostly 

 covered with digital impressions for accommodation of the 

 cerebral convolutions, but along the postero-external 

 margin has a smooth groove through which a large vein 

 runs to torcular herophili, from a small foramen just 

 above the mastoid process of squamous temporal bone. 

 Below this groove, at its outer part, is a rough surface for 

 union with the petrous temporal bone. 



OS FRONTIS (one of which is found on each side of 

 the cranium) forms part of the anterior and of the 

 superior portion of the cranium. It also forms^ the 

 supero-posterior part of the nasal chamber and a consider- 

 able portion of the inner wall of the orbit. So it presents 

 a cranial, a facial, and an orbital plate. The facial plate 

 is quadrilateral, smooth externally, internally^ at its pos- 

 terior part, blends with the cranial plate, at its anterior 

 is roughened, helping to form the frontal sinus. The outer 

 surface is flat, in parts convex, and subcutaneous with 

 exception of its outer margin which is covered by orbicu- 

 laris palpebrarum. From the posterior part of this 

 margin projects the orbital process, a long prominence, 

 flattened from above downwards, externally convex in 

 contact with the orbicularis palpebrarum, intei-nally con- 

 cave in contact with the lachrymal gland, having periorbi- 

 tale attached to its posterior margin. Its outer extremity 

 articulates with the zygomatic process of the squamous 

 temporal bone; its anterior margin forms the superior 



