18 PRACTICAL ANATOMY. 



from each side of this are the superior curved lines. 

 Running from the tubercle to the foramen magnum is a 

 sharp ridge of bone, the external crest, from which passes, 

 midway between the superior curved lines and the fora- 

 men magnum, the inferior curved lines. The bone 

 above the superior curved lines is smooth ; below it is 

 rough, for the attachment of muscles. At the junction 

 of the posterior portion with the basilar process is the 

 foramen magnum, which transmits the spinal cord some 

 nerves, vessels, and membranes. This opening is oval 

 in outline, the larger part of the oval being posterior ; 

 viewed internally, it appears larger than when looked at 

 from the outer surface. Placed at each side, anterior* to 

 its transverse diameter, are the occipital condyles, which 

 approach each other anteriorly, their axes crossing about 

 one inch in front of the foramen magum ; they serve for 

 articulation with the atlas. In front of each condyle is 

 the hypoglossal foramen for the transmission of the hypo- 

 glossal nerve. This foramen is always present, and is 

 of large size. Behind the condyle a foramen is often 

 found, known as the posterior condyloid ; it transmits 

 a vein to the lateral sinus. 



The inner surface of the occipital bone is concave, 

 slightly impressed by the convolutions of the brain, 

 and is divided into four shallow fossae by the occipital 

 cross, the vertical limb of which affords attachment to 

 the falx cerebelli and falx cerebri ; it lodges the superior 

 longitudinal sinus. The horizontal limbs give attach- 

 ment to the tentorium cerebelli and lodge the lateral 

 sinuses. At the point at which they cross, the longi- 

 tudinal and lateral sinuses meet, forming the torcular 

 Herophili. The superior fossae lodge the posterior lobes 

 of the brain ; the inferior fossae, the cerebellum. The 

 superior surface of the basilar process is smooth, con- 



