154 . ^ MANUAL OF ANATOMY 



which coincides with the position of the superior semicircular canal 

 of the internal ear ; and the tegmen tympani. 



Posterior Fossa. — This fossa is on a lower level than the middle. It 

 is limited in front by the dorsum sellae of the sphenoid in the centre, 

 and the superior border of the petrous portion of the temporal at 

 either side. Behind, it is limited by the internal occipital protuber- 

 ance and the groove at either side for the lateral venous sinus, 

 which groove also marks its lateral extent. It lodges the pons 

 Varolii, medulla oblongata, and cerebellum. The bones which 

 form it are as follows : the dorsum sellae of the sphenoid ; the 

 basilar, condylar, and supra-occipital portions of the occipital ; the 

 petrous and mastoid portions of the temporal ; and the postero- 

 inferior angle of the parietal. It presents the following sutures : 

 the occipito-mastoid ; parieto-mastoid ; and petro-basilar. The 

 following parts are to be noted : the basilar groove, the upper 

 part of which lodges the pons Varolii and basilar artery, whilst 

 the lower part contains the medulla oblongata ; the foramen 

 magnum, which transmits the medulla oblongata and its mem- 

 branes, the spinal accessory nerves, and the vertebral, anterior 

 spinal, and posterior spinal, arteries; the anterior condylar 

 foramen, on either side of the foramen magnum, for the hypo- 

 , glossal nerve and a meningeal branch of the ascending pharyngeal 

 artery; the internal occipital crest, which gives attachment to 

 the falx cerebelli, and is occasionally grooved for the occipital 

 process of thf^'r^r^K^r/^^^ ^^^ foramen magnum this crest presents 

 hemisnhprpc^f +J,"!]' ^^^'^'e. receives a part of the vermiform 

 meatus on fl! ^f ^bellum ; the opemT^abellar fossa, which lodge the 

 t~al,' for VtdT T'^^I- ^^ the Veir:^ of th^ internal auditory 

 Wrisber^ ^n/ J. ^^ ^"^ auditory nerves fe ^^^-ous portion of the 

 i inch external f -^ .1 ""^ ^""^^^^ ' ^^^ aqueductus Vfe 5^'^^^ intermedia of 

 the ductus en Inl *^^ .P^^^^ding, for a small artery anZ'^^'-tibuli, about 



thefioccular W^Lrlvl"/' '^l' ''''"^ subarcuata, ?epr"* ^^---' -^ 

 of the petrous Dor^inn I !' '^*^^*"^ ^^^^^ to the s^perfo^P "^^^enting 

 internafauTtor^^^'Ss ,,'d' "^'^^J'^ ^^^ween the oPZ^ "PJ^T^f* 

 foramen or foSm^„^«^Lf aqueductus vestibuli ; and the im^ "f "^^ ^^^ 



externa? coVrtment'" J°SV"'', ^fd^ The por.eCts t 

 become the internal jugular tdn and » '"' ^f""^ ^""^ ' ' 



ascendmg pharyngea artery he mfddl."'"^"'^ '"■*°<='' °f "■-poral 

 the glosso-pharyn|eal, pneumogastrfc f ^H "™P"'">»' transmits^^ea 

 petrosal \"*r-W-rnaf con^aftoe" t &a°st»^?^'y "V'' ^'h 



lets, 

 ata, 



