182 



BONES OP THE CRANIUM. 



FIG. 38. 



Along the sagittal suture, on the interior, is a groove for 

 lodging the superior longitudinal sinus. 



The structure is thin and consists of two compact tables 

 and an intervening diploe. The development takes place by 

 one point of ossification "in each parietal protuberance, com- 

 mencing about the seventh or eighth week. 



The parietal articulates with five bones, the frontal, 

 occipital, temporal, sphenoid, and its fellow. 



Occipital Bone (os occipitis.) The occipital bone is sit- 

 uated at the posterior in- 

 ferior part of the cranium 

 Its form is rhomboidal. It 

 has two surfaces, an ex- 

 ternal and internal. The 

 external is irregularly con- 

 vex, and has near its cen- 

 tre the external occipital 

 protuberance, to which the 

 cervical ligament is at- 

 tached. On either side 

 extends, transversely, the 

 superior transverse ridge, 

 to which the trapezii and posterior bellies of the occipito- 

 frontales muscles are connected. A short distance below is 

 the inferior transverse ridge, and below this again, on the 

 inferior surface is the foramen^nagnum. The space between 

 the two ridges is occupied by the complexi and splenii 

 muscles. The inferior ridge and the space between it and 

 the foramen magnum, gives attachment to the posterior recti 

 and superior oblique muscles. 



The foramen magnum has leading to it from the occipital 

 protuberance, a vertical ridge. Its shape is oval, and it 



FIG. 38 represents the external surface of the Occipital Bone, a Superior 

 semi-circular ridge. 6 External occipital protuberance, c Point where the 

 ligamentum nuchae is attached, d Inferior semi-circular ridge, e Foramen 

 magnum. / Condyle of the right side, g Posterior condyloid foramen, h An- 

 terior condyloid foramen, i Jugular eminence, j Part of jugular foramen. 

 & Basilar process. I Where odontoid ligaments are attached, m Surface for 

 parietal bones, n Surface for mastoid portion of temporal bone. 



