01 



CHAP, in.] SKELETON OF TffE HEAD AND TRUNK. 



parts), and the hyoid bone * seventeen bones in all, Form the 

 skeleton of the face. 



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

 surrounds the great occipital foramen, or foramen magnum (fin}. 

 When 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 



Fig. 31. THE OCCIPITAL. 



A. External surface. 



B. Internal surface. 

 bo. Basi-occipital. 

 c. Condyle. 



cb. Cerebellar fossa. 



eo. Ex-occipital. 

 fm. Foramen magnum. 

 1. Lambdoidal ridge. 

 p. Par-occipital process, 

 so. Supra-occipital. 



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

 forwards. 



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

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

 the quadrangular plate in front (bo) is the basi-occipttal, 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 (I), which descends on each side of the occiput, and is called 

 the lambdoidal 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 basi- occipital 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 here, for the sake of simplicity 

 and clearness, spoken of as one. 



