THE OCCIPITAL BONE. 107 
serve for the attachment of the complexus, obliquus superior, and rectus capitis 
posticus major and minor muscles. 
The internal surface of the squama, concave from side to side and from above 
downwards, is subdivided into four fosse by a erucial arrangement of ridges and 
grooves. The upper pair of fosse lodge the occipital lobes of the cerebrum, the 
lower pair the lobes of the cerebellum. Near the centre of this aspect of the bone 
is the internal occipital protuberance (protuberantia occipitalis interna), an irregular 
elevation, the sides of which are variously channelled according to the disposition 
of the grooves. Leading from this to the hinder margin of the foramen magnum 
is a sharp and well-defined ridge, the internal occipital crest (crista occipitalis 
interna), which serves for the attachment of the falx cerebelli, a process of dura 
mater which separates the two cerebellar hemispheres. Passing upwards from the 
For superior longitudinal sinus and falx Corey Superior angle 
> ~ae 
Cerebral fossa \ 
Internal occipital 
YF yrotuberance 
Torenlar~_ 
For lateral sinus 
and tentorium 
Lateral angle 
Cerebellar fossa 
Internal occipital 
crest 
Groove for 
i Jugular process 
lateral sinus Jugular process 
Posterior condylic 
foramen 
Jugular notch 
Groove for inferior petrosal sinus-~ 
Basilar groove 
Basilar process 
Fic. 83.—OccipiraAL Bone (Inner Surface). 
internal occipital protuberance there is usually a well-marked ridge, to one or other 
side of which, more frequently the right (with the bone in the normal position and 
viewed from behind), there is a well-defined groove, the sulcus sagittalis, the outer 
lip of which is generally less prominent. Placed in this groove is the superior 
longitudinal venous sinus, and attached to the lips is the falx cerebri. At right 
angles to the foregoing, and at the level of the internal occipital protuberance, with 
which they become confluent, are two transverse grooves, the sulci transversi. These 
grooves, which have more or less prominent edges, lie between the upper and lower 
_ pairs of fosse, and serve for the attachment of the tentorium cerebelli as well as 
the lodgment of the lateral blood-sinuses. Commonly the right lateral groove 1s 
confluent with the groove to the right side of the median ridge, but exceptions to 
this rule are not infrequent. The angle formed by the union of the venous sinuses 
lodged in these grooves constitutes the toreular Herophili, which may accordingly 
