THE BASE OF THE SKULL. 109 



meningeal artery, and the prominent spinous process of the sphenoid, which gives 

 attachment to the internal lateral ligament of the lower jaw and the Tensor palati 

 muscle. External to the spinous process is the glenoid fossa, divided into two parts 

 by the Glaserian fissure (page 66), the anterior portion concave, smooth, bounded 

 in front by the eminentia articularis, and serving for the articulation of the condyle 

 of the lower jaw; the posterior portion rough, bounded behind by the tympanic 

 plate, and serving for the reception of part of the parotid gland. Emerging from 

 between the laminae of the vaginal process of the tympanic plate is the stytoid proc- 

 ess, and at the base of this process is the stylo-mastoid foramen, for the exit of the 

 facial nerve and entrance of the stylo-mastoid artery. External to the stylo-mastoid 

 foramen is the auricular fissure, for the auricular branch of the pneumogastric, 

 bounded behind by the mastoid process. Upon the inner side of the mastoid proc- 

 ess is a deep groove, the digastric fossa ; and a little more internally the occipital 

 groove, for the occipital artery. At the base of the internal pterygoid plate is a 

 large and somewhat triangular aperture, the foramen lacerum medium, bounded in 

 front by the great wing of the sphenoid, behind by the apex of the petrous portion 

 of the temporal bone, and internally by the body of the sphenoid and basilar proc- 

 ess of the occipital bone : it presents in front the posterior orifice of the Yidian 

 canal ; behind, the aperture of the carotid canal. The basilar surface of this open- 

 ing is filled in the recent state by fibre-cartilaginous substance ; across its upper 

 or cerebral aspect passes the internal carotid artery. External to this aperture the 

 petro-sphenoidal suture is observed, at the outer termination of which is seen the 

 orifice of the canal for the Eustachian tube and that for the Tensor tympani muscle. 

 Behind this suture is seen the under surface of the petrous portion of the temporal 

 bone, presenting, from within outward, the quadrilateral, rough surface, part of 

 which affords attachment to the Levator palati and Tensor tympani muscles ; exter- 

 nal to this surface the orifices of the carotid canal and the aquaeductus cochleae, 

 the former transmitting the internal carotid artery and the ascending branches of 

 the superior cervical ganglion of the sympathetic, the latter serving for the passage 

 of a small artery and vein to the cochlea. Behind the carotid canal is a large 

 aperture, the jugular foramen, formed in front by the petrous portion of the tem- 

 poral, and behind by the occipital ; it is generally larger on the right than on the 

 left side, and is divided into three compartments by processes of dura mater. The 

 anterior is for the passage of the inferior petrosal sinus ; the posterior, for the 

 lateral sinus and some meningeal branches from the occipital and ascending phar- 

 yngeal arteries ; the central one, for the glosso-pharyngeal, pneumogastric, and 

 spinal accessory nerves. On the ridge of bone dividing the carotid canal from the 

 jugular foramen is the small foramen for the 'transmission of Jacobson's nerve; 

 and on the wall of the jugular foramen, near the root of the styloid process, is the 

 small aperture for the transmission of Arnold's nerve. Behind the basilar surface 

 of the occipital bone is the foramen magnum, bounded on each side by the con- 

 dyles, rough internally for the attachment of the check or odontoid ligaments, and 

 presenting externally a rough surface, the jugular process, which serves for the 

 attachment of the Rectus capitis lateralis muscle and the lateral occipito-atlantal 

 ligament. On either side of each condyle anteriorly is the anterior condyloid fossa, 

 perforated by the anterior condyloid foramen, for the passage of the hypoglossal 

 nerve and a meningeal artery. Behind each condyle is the posterior condyloid 

 fossa, perforated on one or both sides by the posterior condyloid foramina, for the 

 transmission of a vein to the lateral sinus. Behind the foramen magnum is the 

 external occipital crest, terminating above at the external occipital protuberance, 

 whilst on each side are seen the superior and inferior curved lines ; these, as well 

 as the surfaces of bone between them, are rough for the attachment of the muscles, 

 which are enumerated on page 59. 



