os OCCIPITIS. 73 



muscular depression to which the rectus minor posticus is 

 attached on each side near the middle ; and the rectus major 

 posticus, and obliquus superior, near the end. 



Below the protuberance is a spine which passes do\yn the 

 middle of the bone, and at the lower extremity of this spine is 

 the great occipital foramen, which forms the communication 

 between the cavities of the cranium, and the vertebral column. 

 This great opening transmits the medulla spinalis with its 

 membranes, the accessary nerves of Willis, and the vertebral 

 arteries and veins. 



It is rather of an oval form, and the occipital condyles are 

 situated anteriorly on its edges. These condyles are of an 

 irregular oval figure ; they are not parallel, but incline towards 

 each other anteriorly. Their articulating surfaces are oblique, 

 looking downward and outward ; they are received into 

 corresponding cavities of the atlas, or first cervical vertebra, 

 and form with them the articulation of the head and neck. 

 From the oblique position of their articulating surfaces, as well 

 as the length of their ligaments and the inclination of their 

 axes towards each other, it results, that their motion is confined 

 to flexion and extension. On the internal sides of these 

 condyles is a rough surface, to which are attached the strong 

 ligaments that come from the processus dentatus of the second 

 vertebra of the neck. 



Behind each condyle is a depression in which is situated the 

 posterior condyloid foramen, for transmitting the cervical 

 veins ; and at their anterior extremities are two large foramina, 

 (anterior condyloid,) through which pass the ninth pair of 

 nerves. 



On the internal surface of the os occijfitis is the crucial 

 ridge, to which are attached the falx cerebelli or vertical, 

 and the tentorium or horizontal process of the dura mater. 



The groove made by the longitudinal sinus continues from 

 the sagittal suture along the upper limb of this cross. Some- 

 times it is on the side of the ridge, and sometimes the ridge is 

 depressed, and it occupies its place ; at the centre of the cross, 

 where is lodged the torcular Herophili, formed by the 

 7 



