136 



THE SKELETON. 



foramina. From this eminence, the superior division of the crucial ridge runs 

 upward to the superior angle of the bone ; it presents occasionally a deep groove 

 for the superior longitudinal sinus, the margins of which give attachment to 

 the falx cerebri. The inferior division, the internal occipital crest, runs to the 



Fig. 90. Occipital Bone. Inner Surface. 



Inferior Anal? 



posterior margin of the foramen magnum, on the edge of which it becomes 

 gradually lost; this ridge, which is bifurcated below, serves for the attachment 

 of the falx cerebelli. It is usually marked by two small grooves, which com- 

 mence on either side of the posterior margin of the foramen magnum, join 

 together above, and run into the depression for the Torcular Herophili. They 

 lodge the occipital sinuses. The transverse grooves pass outwards to the lateral 

 angles; they are deeply channelled, for the lodgment of the lateral sinuses, 

 their prominent margins affording attachment to the tentorium cerebelli. 1 At 

 the point of meeting of these grooves is a depression, the "Torcular Hero- 

 phili," 2 placed a little to one or the other side of the internal occipital pro- 

 tuberance. More anteriorly is the foramen magnum, and on each side of it, 

 but nearer its anterior than its posterior part, the internal openings of the ante- 



1 Usually one of the transverse grooves is deeper and broader than the other ; occasionally 

 both grooves are of equal depth and breadth, or both equally indistinct. The broader of the 

 two transverse grooves is nearly always continuous with the vertical groove for the superior 

 longitudinal sinus, and occupies the corresponding side of the median line. 



2 "The columns of blood coming in different directions were supposed to be pressed together at 

 this point. 



