THE INTERIOR OF THE SKULL 



193 



the basilar portion of the occipital and the posterior part of the body of the sphenoid 

 form a grooved surface which supports the medulla oblongata and pons; in the 

 young skull these bones are joined by a synchondrosis. This grooved surface is 

 separated on either side from the petrous portion of the temporal by the petro- 

 occipital fissure, which is occupied in the fresh state by a plate of cartilage; the 

 fissure is continuous behind with the jugular foramen, and its margins are grooved 

 for the inferior petrosal sinus. The jugular foramen is situated between the lateral 

 part of the occipital and the petrous part of the temporal. The anterior portion 

 of this foramen transmits the inferior petrosal sinus; the posterior portion, the 

 transverse sinus and some meningeal branches from the occipital and ascending 

 pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, 

 and accessory nerves. Above the jugular foramen is the internal acoustic meatus, 

 for the facial and acoustic nerves and internal auditory artery; behind and lateral 



Nasal bone 



Frontal process 



of maxilla 

 Inf nasal concha 



Palatine bone 

 FIG. 194. Sagittal section of skull. 



to this is the slit-like opening leading into the aqueeductus vestibuli, which lodges 

 the ductus endolymphaticus ; while between these, and near the superior angle of 

 the petrous portion, is a small triangular depression, the remains of the fossa sub- 

 arcuata, which lodges a process of the dura mater and occasionally transmits a small 

 vein. Behind the foramen magnum are the inferior occipital fossae, which support 

 the hemispheres of the cerebellum, separated from one another by the internal 

 occipital crest, which serves for the attachment of the falx cerebelli, and lodges 

 the occipital sinus. The posterior fossae are surmounted by the deep grooves for 

 the transverse sinuses. Each of these channels, in its passage to the jugular foramen, 

 grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the 

 temporal, and the jugular process of the occipital, and ends at the back part of 

 the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, 

 the orifice of the mastoid foramen may be seen; and, just previous to its termina- 

 tion, the condyloid canal opens into it ; neither opening is constant. 

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