THE BONES OF THE HEAD 57 



The Occipital Bone. 



The occipital bone is so named because it is situated against the 

 posterior and inferior parts of the cranium. It is quadrilateral 

 and curved, its long axis extending from above downwards 

 and forwards. At its lower and anterior part there is a large 

 opening, called the foramen magnum, by which the cranial cavity 

 communicates with the spinal canal. The bone is divisible into four 

 parts, which meet around this opening. The part behind is called 

 the tabular portion, that in front ihe basilar process, and the part at 

 either side the condylar portion. 



The tabular portion presents two surfaces, three angles, and four 

 borders. The posterior or external surface is convex and projected 

 at its centre into the external occipital protuberance, from which a 

 median ridge, called the external occipital crest, passes dowTiwards 

 and forwards to the foramen magnum. The protuberance and crest 

 give attachment to the ligamentum nuchae. Arching outwards on 

 either side from the protuberance to the lateral angle there is the 

 superior curved line, the convexity of which is directed upwards. 

 The two lines with the protuberance divide this surface into an upper 

 or interparietal and a lower or supra-occipital part. A little above 

 each superior curved line there is the highest curved line, which has 

 a bold cur\'e with the convexity upwards, and gradually subsides 

 in the superior curved line externally. Between these two lines 

 there is a semilunar area, over which the bone is smooth and dense. 

 The highest curs-ed line gives attachment to the epicranial apo- 

 neurosis internally, and to fibres of the occipitalis externally. The 

 superior curved line gives origin over about its inner third to the 

 trapezius, and externally to fibres of the occipitalis, whilst over its 

 outer half, or more, it gives insertion to the stemo-cleido-mastoid, 

 immediately below which the splenius capitis is inserted over about 

 the outer third. The portion of this surface above the highest 

 curved lines is smooth, convex, and covered by the epicranial apo- 

 neurosis. The portion below the superior curved lines, which is 

 rough and irregular, is divided into two equal lateral parts by the 

 crest, and each of these is subdivided into an upper and lower 

 portion by the inferior curved line, which extends from the centre 

 of the crest to the extremity of the jugular process. The space 

 between the superior and inferior curved lines gives insertion 

 internally to the complexus, and externally, from above down- 

 wards, to the splenius capitis and obliquus capitis superior. The 

 inferior curved line gives insertion over its outer part to the rectus 

 capitis posticus major. The inner third of this line and the surface 

 between that extent of it and the foramen magnum give insertion 

 to the rectus capitis posticus minor. 



The anterior or internal surface is irregularly concave and divided 

 into four fossae by two ridges— a longitudinal, extending from the 

 superior angle to the foramen magnum, and a transverse, extending 

 from one lateral angle to the other. At the point where these two 



