174 



HUMAN ANATOMY. 



the latter ridge is wanting, the groove of the lateral sinus curving over the jugular 

 pro-ess The upper surface of the lateral portion of the process shows on its inner 

 side the entrance of the anterior condyloid foramen, which is really a short canal. 

 Above and anterior to this is a slight swelling, the jugular tubercle. The upper 

 surface of the jugular process is marked by the termination of the groove of the 

 lateral sinus, which curves round an upward projectfon of the process. In some 

 cases as just mentioned, the groove is depressed into a deep hollow. 1 he inner 

 opening of the posterior condyloid foramen, when present, is connected with the 



lateral sinus. , , , t i i n d i v 



The squamous portion ' forms the lower and back part of the skull, below it 

 contributes the posterior boundary of the foramen magnum and joins the exoccipitals^ 

 The lateral borders meet above at a sharp angle. These borders may be subdivided 

 into a lower part, which ascends nearly vertically in articulation with the mastoid 

 part of the temporal, and into a higher part, very serrated and joining the parietal. 

 A slight angle lies on either side at the junction of these two divisions. 



Fig. 193. 



Internal occipital protuber- 

 ance 



Superior occipital 

 fossa 



Groove for right 

 lateral sinus 



Inferior occipital 

 fossa 



Groove for left 

 lateral sinus 



Jugular process' 



Jugular notch 



Groove for lateral sinus 

 Jugular tubercle 



Anterior condyloid foramen, probe 

 in canal 



Occipital bone, internal surface, from before. 



The posterior surface is marked by a prominence, somewhat below the 

 middle, the external occipital protuberance,"^ to which is attached the ligamentum 

 nuchae. This tuberosity varies greatly in development. From it the stiperior curved 

 line^ extends laterally to the above-mentioned angle. To this line are attached a 

 series of muscles which form the contour of the back of the neck, chiefly the trapezius 

 and part of the sterno-cleido-mastoid. A short and varying distance above the supe- 

 rior ridge is often seen the so-called highest curved line^ It is usually very faint, 

 and may curve down to the external occipital protuberance, or pass above it. The 

 epicranial aponeurosis and part of the occipitalis spring from this line. The surface 

 of the bone above the level of the protuberance is smooth ; below it is rather rough 

 and irregular. The torus occipitalis transversiis is an occasional prominence in- 

 volving the protuberance and extending laterally along the superior curved line. 

 It sometimes involves the space between that line and the highest one. The upper 

 border of the swelling may have a median concavity. In the mid-line a slight ridge, 



'Squamosa occipitalis. ' Protuberantia occipitalis externa. ^Linea nuchae superior. ^Linea nuchae suprema. 



