THE OCCIPITAL BONE 



53 



The curved lines and the areas thus mapped out between and below them give attachment 

 to several muscles. To the superior nuchal line are attached, medially the trapezius, and 

 laterally the occipitalis and sterno-cleido-mastoid; the area between the superior and inferior 

 curved Unes receives the semispinalis capitis (complexus) medially, and splenius capitis and 

 obliquus capitis superior laterally; the inferior nuchal line and the area below it afford insertion 

 to the rectus capitis posterior minor and major. 



The anterior or cerebral surface is deeply concave and marked by two grooved 

 ridges which cross one another and divide the surface into four fossae of which 

 the two upper, triangular in form, lodge the occipital lobes of the cerebrum, and 

 the two lower, more quadrilateral in outline, the lobes of the cerebellum. The 

 vertical ridge extends from the superior angle to the foramen magnum and the 

 transverse ridge from one lateral angle to the other, the point of intersection being 

 indicated by the internal occipital protuberance [eminentia cruciata]. The 



Fig. 66. — Occipital Bone, Cerebral Surface. 



Superior angle 



For superior sagittal sinus and falx 

 cerebri 



Cerebral fossa 



Groove for transverse sinus 



( 



Lateral angle 



Cerebellar fossa 



Groove for transverse sinus 



Jugular process — 

 For petrosal 



BASI-OCCIPIT AL 



upper part of the vertical ridge is grooved [sulcus sagittalis] for the superior 

 sagittal (longitudinal) sinus and gives attachment, by its margins, to the falx 

 cerebri; the lower part is sharp and known as the internal occipital crest, and 

 affords attachment to the falx cerebelli. Approaching the foramen magnum 

 the ridge divides, and the two parts become lost upon its margin. The angle 

 of divergence sometimes presents a shallow fossa for the extremity of the vermis 

 of the cerebellum, and is called the vermiform fossa. The two parts of the 

 transverse ridge are deeply grooved [sulcus transversus] for the transverse 

 {lateral) sinuses, and the margins of the groove give attachment to the tentorium 

 cerebelli. To one side of the internal occipital protuberance is a wide space, 

 where the vertical groove is continued into one of the lateral grooves (more 

 frequently the right), and this is termed the torcular Herophili; it is sometimes 

 exactly in the middle line. 



The squamous portion has three angles and four borders. The superior angle 

 forming the summit of the bone is received into the space formed by the union of 

 the two parietals. The lateral angles are very obtuse and correspond in situatio n 

 with the lateral ends of the transverse ridges. Above the lateral angle on each 

 side the margin is deeply serrated, forming the lambdoid or superior border 

 which extends to the superior angle and articulates with the posterior border of 

 the parietal in the lambdoid suture. The mastoid or inferior border extends 



