Chap. 5.] Ethmoid Bout. roi 



cular ligament which pafles from the circumference of 

 the foramen to the firft vertebra. On the in fide of 

 the occipital bone 'are feveral ridges and furrows ; to 

 one of the ridges is fixed the pofterior part ofthefalx, 

 and the furrows receive the finufes which run in this 

 part of the cranium. The ridges of this bone form a 

 crofs, and round the middle of the crofs there are four 

 large depreffions, feparated by its limbs j the two up- 

 per depreflions being formed by the pofterior part of 

 the brain, and the two lower by the cerebellum. The 

 inner furface of the cuneiform procefs is hollowed for 

 the reception of the medulla oblongata and the bafilar 

 artery. Befides the great foramen, there are feveral 

 other perforations in this bone, or between it and the 

 adjoining bones, for the paJTage of nerves and blood- 

 vefiels. The occipital bone at its tipper part, where it 

 is chiefly expofed to injury, is very thick and ftrong, 

 but lower down, where it is protected by the ftrong and 

 thick mufcles which are inferted into it, it is often very 

 thin. The occipital bone is connected above to the 

 ofTa parietalia by the lambdoidal future ; laterally to 

 the temporal bones by a continuation of the fame fu- 

 ture ; below it is firmly connefted by an union of fub- 

 ftance to the fphenoid bone, by means of the cuneiform 

 proct-fs. 



The os ethmoides, or fieve-like bone, derives its 

 name from the numerous fmall apertures with which 

 it is pierced at its fore part. From the middle of the 

 internal fide of the lamella, which is fo full of holes, 

 a thick procefs rifes upwards j and being higheft at the 

 fore part, gradually becomes lower as it is extended 

 backwards. From a fancied refemblance of this pro- 

 cefs to a cock's comb, it has been called the crifta- 

 galli. The falx is connected to its ridge, and to the 

 unperforated part of the cribrfcrm plate. All the pro- 

 H 3 minences. 



