THE OCCIPITAL BONE. 123 



rectus capitis lateralis muscle. The superior aspect of the lateral part displays on 

 either side of the foramen magnum an elevated surface of oval form, the tuberculum 

 jugnlare ; this corresponds to the part of the bone which bridges over the canal 

 for the hypoglossal nerve. Its upper surface in many instances displays an oblique 

 groove running across it; in this are lodged the glosso-pharyngeal, vagus, and 

 accessory nerves. The jugular process is deeply grooved superiorly for the lower 

 part of the transverse blood sinus, or sigmoid sinus, which here turns round the 

 anterior free edge of the process into the jugular foramen. Joining this, close to 

 its medial edge, is the opening of the canalis condyloideus, when it exists. 



The basilar part of the occipital bone extends forwards and upwards 

 from the foramen magnum. Its anterior extremity is usually sawn across, as, 



Groove for superior sagittal sinus and falx cerebri Superior angle 



Cerebral fossa x ,i>tmmi 



^ggagmffi^fcg-^ 



\X^B^ESM|^H ^*Wli Internal occipital 



Depression for confluens ^j^C / protuberance 



sinuum (O.T. tor- 

 cular Herophili)" 



Groove for trans verse 

 sinus and tcntorium 

 cerebelli 



Lateral angle 



Internal occipital 

 crest 



Jugu.ar process 



^K mr/^^^ X Canalis condyloideus 



BHHl ^|B ""' 'f JF Tuberculum jugulare 



ve for inferior petrosal sinus - 



^^^^^^^^^^^ ""^Basilar groove 



Basilar part 



FIG. 134. OCCIPITAL BONE (Cerebral Surface). 



after adult life, it is necessary to sever it in this way from the sphenoid, the 

 cartilage uniting the two bones having by that time become completely ossified. 

 Broad and thin posteriorly, it narrows at the sides and thickens vertically in front 

 where on section it displays a quadrilateral form. Projecting from its inferior 

 surface some little distance anterior to the foramen magnum is the pharyngeal 

 tubercle to which the fibrous raphe of the pharynx is attached ; on each side of 

 this the longus capitis and rectus capitis anterior muscles are inserted. The 

 superior surface forms a broad and shallow groove which slopes upwards and 

 forwards from the thin anterior margin of the foramen magnum ; in this rests the 

 medulla oblongata. On each side its lateral edges are faintly grooved for the 

 inferior petrosal venous sinuses, below which the lateral aspect of the bone is rough 

 for the cartilage which unites it to the sides and apex of the petrous part of the 

 temporal bone. 



The foramen magnum, of oval shape, so disposed that its long axis lies in the 



