56 THE SKELETON. 



condyles, by which the bone articulates with the atlas. These processes are known 

 as the condylar portions. It presents for examination two surfaces, four borders, 



and four angles. . f , , 



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, and, descending from it as far as the foramen, a vertical 

 ridge the external occipital crest. This protuberance and crest give attachment 

 to the Lio-amentum nuchse, and vary in prominence m diiferent skulls Passing 

 outward from the occipital protuberance is a semicircular ridge on each side, the 

 superior curved line. Above this line there is often a second less distinctly marked 

 ricke called the highest curved line (linea supremo) ; to it the epicranial aponeurosis 

 is attached. The bone between these two lines is smoother and denser than the 

 rest of the surface. Running parallel with these from the middle of the crest is 

 another semicircular ridge on each side, the inferior curved lines. The surface of 

 the bone above the linea suprema is rough and porous, and in the recent state is 

 covered by the Occipito-frontalis muscle, while the superior and inferior curved 

 lines, together with the surfaces of bone between and below them, serve for the 

 attachment of several muscles. The superior curved line gives attachment inter- 

 nally to the Trapezius, externally to the muscular origin of the Occipito-frontalis, 

 and to the Sterno-cleido-mastoid to the extent shown in Fig. 23 ; the depressions 

 between the curved lines to the Complexus internally, the Splenius capitis and 

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

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



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

 before backward. It transmits the medulla oblongata and its membranes, the 

 spinal accessory nerves, the vertebral arteries, the anterior and posterior spinal 

 arteries, and the occipito-axial ligaments. Its back part is wide for the transmission 

 of the medulla, and the corresponding margin rough for the attachment of the dura 

 mater enclosing it ; the fore part is narrower, being encroached upon by the con- 

 dyles ; it has projecting toward 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, oval, or reniform in shape, and directed downward and outward ; they 

 converge in front, and encroach slightly upon the anterior segment of the foramen. 

 On the inner border of each condyle is a rough tubercle for the attachment of the 

 ligaments (check] which connect this bone with the odontoid process of the axis ; 

 whilst external to them is a rough tubercular prominence, the transverse or jugular 

 process, channelled in front by a deep notch, which forms part of the jugular 

 foramen or foramen lacerum posterius. The under surface of this process presents 

 an eminence which represents the paramastoid process of some mammals. The 

 eminence is occasionally large, and extends as low as the transverse process of the 

 atlas. This surface affords attachment to the Rectus capitis lateralis muscle and 

 to the lateral occipito-atlantal ligament ; its upper or cerebral surface presents a 

 deep groove which lodges part of the lateral sinus, whilst its external surface is 

 marked by a quadrilateral rough facet, covered with cartilage in the fresh state, and 

 articulating with a similar surface on the petrous portion of the temporal bone. On 

 the outer side of each condyle, near its fore part, is a foramen, the anterior con- 

 dyloid ; it is directed downward, outward, and forward, and transmits the hypo- 

 glossal nerve, and occasionally a meningeal branch of the ascending pharyngeal 

 artery. This foramen is sometimes double. . Behind each condyle is a fossa, 1 some- 

 times perforated at the bottom by a foramen, the posterior condyloid, for the trans- 

 mission of a vein to the lateral sinus. In front of the foramen magnum is a strong 

 quadrilateral plate of bone, the basilar process, wider behind than in front ; its 

 under surface, which is rough, presenting in the median line a tubercular ridge, 



1 This fossa presents many variations in size. It is usually shallow, and the foramen small ; occa- 

 sionally wanting on one or both sides. Sometimes both fossa and foramen are large, but confined to 

 one side only ; more rarely, the fossa and foramen are very large on both sides. 



