CHAP. III.] 



SKELETON OF THE HEAD AND TRUNK. 



61 



parts), and the liyoid bone* — seventeen bones in all, form the 

 skeleton of the face. 



§ 23. The OCCIPITAL rone is of course that of the occiput, and it 

 surrounds the great occipital foramen, or foramen magnKm {fin). 

 AVhen detached, it is seen to be somewhat lozenge-shaped, but 

 rounded above and truncated below. It is made up of a crescentic 

 plate of bone extending above and beside the foramen magnum, and 

 of another narrower and quadrangular plate of bone, which, joining 



A. External surface. 



B. Internal surface. 

 io. Basi-occipitiil. 

 c. Ci)ndyle. 



t?). Cerebellar fossa. 



Fis- 31.— The Occipital. 



B 



CO. Ex-occipital. 

 fm. Foramen niagnnm. 

 /. Laniljiloiclal riilge. 

 j>. Par-occipital proces.s. 

 so. Supra-occipital. 



the other, bounds the foramen magnum below, and thence extends 

 forwards. 



The part above the great foramen (so) is the supm-occipital bone, 

 while the parts placed one on each side of it (eo) arc the cx-occipitah, 

 the quadrangular plate in front {ho) is^ the hasi-occipitnl, and these 

 four are all separate and distinct bones in the young kitten. 



The margin of the supra-occipital projects outwards as a bony 

 ridge (/), wdiich descends on each side of the occiput, and is called 

 the lamhdoidal ridge or occipital ridge, and affords a special surface 

 for muscular attachment. The outer surface of the supra- occipital 

 is undulating and more or less convex. Its inner surface presents 

 shallow depressions or fossae, one of which {cb) is placed medianly 

 above the foramen magnum, and lodges the middle portion of that 

 part of the brain called the cerebellum. 



The hasi-occip>ital narrows somewhat as it advances forwards. Its 

 upper surface exhibits a smooth concavity, the basilar groove, which 

 supports that part of the nervous centres termed the " medulla 



oblongata " 



Each part of the bone which bounds the foramen magnum on 

 each side, i.e., each ex-occipital, supports one of the condyles before 



* Really made up of .several distinct bones ; but lieie, for the sake of simplicity 

 and clearnes.s, spukeu of a.s oue. 



