78 ELEMENTARY ANATOMY. [LESS. 



at their sutures) it comes away in one piece with a very large 

 and irregularly shaped bone, the " sphenoid," with which it is 

 connected by a solid bony isthmus (forming the middle of 

 the base of the skull), which isthmus has to be sawn across 

 in order to detach the occipital bone for the purpose of 

 anatomical study. Above the occipital foramen the occipital 

 bone forms an expanded plate (the squama), marked exteriorly 

 by transversely extended " curved lines." 



FIG. 85. OUTER SURFACE OF MAN'S OCCIPITAL BONE. 



lo, basilar part or body of the bone which unites with the body of the sphenoid ; 

 c, one of the two condyles ; /, superior curved line ; /', inferior curved line ; 

 pm, one of the jugular eminences ; so, the squama, or expanded upper part 

 of the occipital ; i, condyloid foramen ; fin, foramen magnum. 



The " condyles," before noticed, are attached to this bone, 

 and external to each is a slight roughened process called the 

 "jugular" eminence, because it borders that aperture of the 

 skull through which the jugular vein comes out. Behind 

 each condyle is a small hole, or foramen, which allows the 

 hypoglossal 1 nerve to pass out from the brain. 



The occipital unites, as has been said, with the sphenoid in 

 front. Above this junction it articulates on each side with 

 the bone from which springs the mastoid process and zygoma, 



1 For this and other nerves see Lesson VIII. 



