Skull and Hyoid 



215 



In addition to the above, the upper surface has ill-defined markings, due to the 

 pressure of the lower convolutions of the temporo-sphenoidal lobe of the brain. 



The upper and inner surfaces are separated by the upper margin to which the 

 Tentorium cerebelli is attached : the superior petrosal sinus runs in a groove along it 

 between the layers of the tentorium, the groove extending from the lateral sinus behind 

 to the depression for the ganglion in front. The sinus runs forward above the level 

 of the fifth nerve, which is below the tentorium, so it does not touch the petrous bone 

 at or in front of the depression for the nerve. 



The apex of the petrous is rough with bony projections : it forms the posterior 

 boundary of the foramen laceram, and the size of the foramen depends on the extent 

 to which the ossification of the petrous has extended forward. A ligamentous band, 

 petro-clinoid, passes from the topmost point of the 

 apex to the posterior clinoid process, and the sixth 

 nerve passes under the outer part of this ligament ; 

 ossification may extend into the ligament, which 

 then forms a little point of bone on the apex (Fig. 

 176), overhanging a groove in which the nerve rests. 



The outer border of the upper surface corre- 

 sponds with the superior petro-squamous suture. 



Dura mater is applied to the upper and inner 

 surfaces of the petrous. Between it and the bone 

 of the upper surface lie the ganglion (in its cavum 

 of dura mater) and the superficial petrosal nerves. 

 On the inner aspect the dura mater is turned into 

 the internal meatus with the nerves, which pierce 

 it in the meatus, and also into the aquaeductus 

 cochleae, where the ductus cochleae passes through 

 it. It has the ductus endolymphaticus between it 

 and the bone, also the petrosal and lateral sinuses 

 and the small vein issuing from the cochlear 

 foramen : it turns into the front part of the 

 jugular foramen to form sheaths for the nerves 

 passing through this opening. 



The styloid process projects downwards, inwards and forwards from the lower 

 aspect of the bone, emerging between the tympanic plate and the petrous, so that the 

 jugular foramen is just internal to it and the stylo-mastoid foramen immediately 

 behind it. It varies in length and has the stylo- hyoid ligament continuous with its 

 extremity. Its base is fused with the petrous bone in the back wall of the tympanum. 



This embedded portion is termed the tympano-hyal, the bony process is the stylo-hyal, the 

 ligament the epi-hyal, and the lesser cornu and upper part of body of hyoid are the cerato-hyal 

 and basi-hyal respectively ; these are all modifications of the bar of the second visceral arch in 

 continuity. 



The Stylo-pharyngeus arises from the inner side of the base of the process- 

 therefore in relation with the internal jugular vein ; the Stylo-hyoid arises from its 

 posterior aspect about half-way down, and the Stylo-glossus from its tip and from the 

 Stylo-hyoid ligament. The process with its muscles and ligament constitute a mass of 

 tissues passing with a general direction downwards, forwards and inwards and conse- 

 quently (Fig. 205) lying in antero-lateral relation to the carotid sheath, a fact that can 

 be at once appreciated on looking at the skull. 



- f&lopii 



Aw. cri frau sip? 



rri'sh. 

 faiti form's. 

 CrilrosA inf. 



fonanen sitjgt&rr, 



FIG. 177. Plan of fundus of right 

 internal auditory meatus. This 

 is divided by a " crista falci- 

 formis " into upper and lower 

 areas. The upper area has an 

 opening for the seventh nerve in 

 front, and others behind for 

 nerves to the upper and outer 

 semicircular canals and utricle ; 

 in the lower part are foramina 

 for cochlear nerves in front, and 

 for nerves to saccule and posterior 

 canal (foramen singulare) behind. 

 The fundus may be barely visible, 

 or, as in the specimen from which 

 this was drawn, may be seen with- 

 out much trouble. 



