24 



BONES OF THE HEAD. 



when adjusted with its fellow, it forms a deep groove for the longitu- 

 dinal sinus.^ The parietal foramen, '^ transmitting an emissary 

 of Santorini, opens in this groove. The inferior edge is short, con- 

 cave, and squamous, articulating with the temporal. The anterior 

 inferior angled is long and pointed ; the posterior inferior^ angle 

 is very obtuse, and deeply grooved on its internal surface for the 

 lateral sinus. 



OCCIPITAL BONE. 



Placed at the posterior and inferior part of the head, is of an oval 

 or trapezoidal shape. 



The external surface is convex and rough in some parts ; near its 

 middle is a prominence called the external occipital cross,^ from 

 which there proceeds on each side a semicircular ridge, ^ to which 

 is inserted the sterno-cleido mastoideus muscle, and from which arise 

 the trapezius and occipital frontalis. About one inch below is an- 

 other semicircular ridge* for the insertion of the superior oblique 

 muscle. Between this ridge and the foramen magnum, the space is 

 occupied by the recti postici muscles. Reaching from the external 

 occipital cross is a vertical ridge^ extending to the foramen magnum, 

 into which is inserted the ligamentum nuchse. A space between the 

 sifperior and inferior semicircular ridges is occupied by the insertion 

 of the splenius and complexus muscles. 



The fora77ien ?nagnu??i^ is oval, its antero-posterior diameter being 

 the largest; it transmits the medulla oblongata, spinal accessory 

 nerves, and vertebral vessels. On either side of the foramen is the 

 condyloid process,^ an oblong convex surface converging towards its 

 fellow, by which the head articulates with the atlas. The anterio?' 

 condyloid foramen^ transmits the hypoglossal or ninth nerve, the 

 posterior condyloid foramen^ a vein to the lateral sinus. 



In front of the foramen mag- 

 num is the basilar process,^^ the 

 extremity of which articulates 

 with the sphenoid ; the inferior 

 surface receives the insertion of 

 the recti postici and superior con- 

 strictor muscle of the pharynx ; 

 the superior surface is concave 

 and contains the medulla oblon- 

 gata. 



The internal surface is con- 

 cave and about its middle has 

 dLninternaloccipitalcvoss,wh\ch. 

 is more prominent than the ex- 

 ternal ; from it there diverge 

 three grooves, containing the two 

 lateral and the superior longitu- 



