58 OSTEOLOGY. 



The External Surface is convex. Midway between the summit of the bone 

 and the posterior margin of the foramen magnum is a prominent tubercle, the 

 external occipital protuberance, for the attachment of the Ligamentum nuchse ; and 

 descending from it, as far as the foramen, a vertical ridge, the external occipital 

 crest. This tubercle and crest vary in prominence in different skulls. Passing 

 outwards from the occipital protuberance on each side are two semicircular ridges, 

 the superior curved lines ; and running parallel with these from the middle of the 

 crest, are the two inferior curved lines. The surface of the bone above the supe- 

 rior curved lines is smooth on each side, and in the recent state is covered by the 

 Occipito-frontalis muscle, whilst the ridges, as well as the surface of the bone 

 between them, serve for the attachment of numerous muscles. The superior 



Fig. 22. Occipital Bone. Outer Surface. 



curved line gives attachment internally to the Trapezius, externally to the Occi- 

 pito-frontalis, and Sterno-cleido-mastoid, to the extent shown in the figure. The 

 depressions between the curved lines to the Complexus internally, the Splenius 

 capitis and Obliquus superior externally. The inferior curved line, and the 

 depressions below it, afford insertion to the Eectus capitis posticus, major and minor. 

 The foramen magnum is a large oval aperture, its long diameter extending 

 from before backwards. It transmits the spinal cord and its membranes, the 

 spinal accessory nerves, and the vertebral arteries. Its back part is wide for the 

 transmission of the cord, and the corresponding margin rough for the attachment 

 of the dura mater inclosing it ; the forepart is narrower, being encroached upon 

 by the condyles ; it has projecting towards it from below the odontoid process, 

 and its margins are smooth and bevelled internally to support the medulla 

 oblongata. On each side of the foramen magnum are the condyles for articulation 

 with the atlas ; they are convex, oblong or reniform in shape, and directed down- 

 wards and outwards; they converge in front, and encroach slightly upon the 

 anterior segment of the foramen. On the inner border of each condvle is a rough 



