46 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 48. — The occipital bone seen from behind (f). 

 Fig. 49. — The occipital bone seen from in front (f). 

 Fig. 50. — The occipital bone seen from below (f). 



Fig. 51.— The occipital and sphenoid bones seen from above (f). The right anterior clinoid process is 

 fused with the middle one. 



Upon the outer margins of the lateral portions of the bone, projecting toward the temporal 

 bone, there is a prominence, the jugular process (Figs. 48, 49, 50, and 51), in front of which 

 is situated a notch, the jugular notch, which is subdivided by a small intra jugular process (Figs. 

 50 and 51), into a small anterior and a larger posterior compartment. By apposition of the 

 notches to corresponding notches of the temporal bone there is formed the jugular foramen 

 (Figs. 43 and 44), which is divided into two compartments by a ligament extending between 

 the corresponding intrajugular processes (see page 55). 



The inner or cerebral surface of the lateral portion of the occipital exhibits a blunt pro- 

 tuberance, the jugular tubercle (Fig. 51), above and to the outer side of the internal orifice of 

 the hypoglossal canal, which consequently passes through the lateral portion of the bone, below 

 the jugular tubercle and above the condyle. Beside the jugular process and beginning in the 

 jugular notch is seen the commencement of the sigmoid groove (see page 43), which curves over 

 the cerebral surface of the jugular process. 



The largest portion of the occipital bone is formed by the squamous portion, which is flat 

 and moderately curved, and in which an internal and an external surface can be recognized. 

 It is bounded by the occipitomastoid suture, forming the mastoid border, and by the lambdoid 

 suture, forming the lambdoid border, and its apex is situated at the posterior extremity of the 

 sagittal suture. 



The most striking formation upon the rather markedly concave internal or cerebral surface 

 (Fig. 49) is the crucial eminence, the ridges of which form four shallow fossae, two superior 

 occipital fossa and two inferior occipital fossa*. The middle of the cross is formed by the internal 

 occipital protuberance, while the inferior median limb, the internal occipital crest, passes to the 

 posterior margin of the foramen magnum. The remaining three limbs are grooves produced 

 by the venous sinuses of the dura mater; the two lateral ones are called the transverse grooves 

 and the superior one is the posterior extremity of the sagittal groove (see page 44). 



The external surface of the squamous portion (Fig. 48) is markedly convex in both the 

 sagittal and transverse directions, and is divided into two surfaces, an inferior nuchal surface 

 (planum nuchale), roughened for the insertion of numerous muscles, and a superior smoother 

 triangular occipital surface (planum occipitale). These two surfaces are separated by the 

 superior nuchal line, a roughened ridge for muscular attachment, which passes in a curved 

 direction from the external occipital protuberance to the occipito-mastoid suture, and a short 

 distance above the linca superior we observe the somewhat more sharply curved linea suprema. 



The entire planum nuchale, from the external occipital protuberance to the foramen mag- 

 num, is traversed by the external occipital crest. From about the middle of this crest, and parallel 

 to the linea suprema, there passes outward the inferior nuchal line, upon which there are fre- 



