68 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



line is the groove for the cartilaginous part of the Eusta- 

 chian tube. Between the apex of the petrous, the basilar 

 process, and the sphenoid is the foramen lacerum (this is the 

 only foramen properly called "lacerated"). This with the 

 petrobasilar fissure is filled with fibrous tissue, and may con- 

 tain Wormian bones. Passing back and out from this is the 

 petrosphenoidal fissure, the styloid and vaginal processes, 

 and the stylomastoid foramen; more internally are the anterior 

 condylar foramina and the jugular fossa. This fossa is divided 

 into three compartments by processes of the dura mater. The 

 inferior petrosal sinus is in the anterior one, the lateral sinus, 

 some ascending pharyngeal and occipital arteries in the pos- 

 terior one, and the ninth, tenth, and eleventh cranial nerves 

 in the middle one. 



Other points have been described with the temporal bone. 



The posterior division presents on either side of the foramen 

 magnum the occipital condyle, jugular process, occipital 

 sulcus, digastric fossa, and mastoid process. Behind the 

 foramen magnum is the tabular part of the occipital up to 

 the superior curved line. Into this posterior division are 

 inserted all the muscles running up to the skull from the ribs, 

 spines, and transverse processes. 



THE INTERIOR OF THE CRANIUM 



The interior of the cranium presents impressions for the 

 cerebral convolutions. The thickness of the skull-cap, or 

 calvaria, is f to J inch. The base of the skull varies in thick- 

 ness, thinnest at the cribriform and orbital plates, where there 

 is no diploe; also thin in the inferior occipital fossa, in the 

 squama, and glenoid fossa. The inner surface of the calvaria 

 is dome-like, formed by the frontal, parietal, and occipital 

 bones. It is marked by the superior longitudinal sulcus, small 

 meningeal grooves, and Pacchionian fossae. The only apertures 

 are the inconstant parietal foramina. 



THE INTERNAL BASE OF THE SKULL 



This surface is divided into three fossae anterior, middle, 

 and posterior. 



The anterior fossa is formed by the orbital plates of the 

 frontal, the cribriform of the ethmoid, the small wings and 



