39 '2 THE SKIN AND THE SENSE-ORGANS. 



by a bony ridge^ which, marks the position of the anterior semi- 

 circular canah Posteriorly and medianly it is separated from the 

 posterior surface by a cartilaginous ridge, running from above, 

 downwards and outwards, which marks the position of the posterior 

 jTjo- 244. semicircular canal. The cartilaginous 



aw hinder root of the j^rocessus sqiiamosus 



olf-^ y "'^^^^^ <:^Zr^ proof ici arises in the cartilaginous ridge 

 ^^ just mentioned, and runs outwards and 



•^;^^ I l^^ forwards, covering the external semi- 



jp^ ( '^ ^ ^ circular canal. 



\ V '^/ / ^y^^ The lower half of the supero-external 



>s;:::p=^ ^^'(^ surfacc (under the processus sfptamosus) 



7zn. is irregularly concave; immediately 



Antero-postei-ior section throiigh l;e ^^^^dç^. the . WrOC. SqiiamOSUS is a shalloW 

 capsule of the right labyrinth 01 _ -^ ... 



liana esadcnta ; after Retzius. En- groOVC in the prootic ; it is COUtiuued 



larged five times. ,^ • -i ^ j^ l^ • ^ j? 



. , ^ , , on the exoccipital to the lugular lora- 



ac. Aqnaeductus cochleae. J- _ 00 



av. Aqnaeductus vestibuii. men. The remaining part of this sur- 



cp. Posterior semicircular canal. „ • 1 c i i j.-i i 



era. CanaJis rami anterioris acustici. taCC COUSlsts Ot a rOUndcd Cartilage, aUCl 



^r Sne2rartundf """' '"'"'"''' ^^ P^rt of the primordial-crauiimi car- 

 fsc. Fovea saccuu et cochleae. tilagc betwccu the prootic and the 



ft. Trigeminal foramen. • -j i j • i -x i n 



Un. Cartilaginous suture. exoccipital j posteriorly it lias a small 



t'r. Prootk!"""^' oval 2,^eYim:e, the foramen ovale {fenestra 



lis. Para.sphenoid. vesUbuIare), whicli with the groove is 



covered by the colvwella. Above the aperture the cartilage narrows 

 and is continued to the processtis squamosus. 



(2) The posterior surface is directly continuous with the supero- 

 external surface, and is formed by the exoccipital. This surface lies 

 behind the ridge formed by the posterior semicircular canal, it is 

 concave, and has two small apertures, separated by a narrow, bony 

 process, and situated near the jugular foramen ; these are the 



foramen rotnndum, [fr.) and the aquaeduclas cochleae {ac.\ 



(3) The anterior surface is altogether bony and formed by the 

 prootic (/«•.); the anterior surface of this part of the wall is continuous 

 with the surface of the cranium, and abuts on to the large tri- 

 geminal foramen (//.); below it is continuous with the under 

 surface of the cranium, below and externally it articulates with the 

 pterygoid. 



(4) The interno-inferior surface is as a whole hollowed in- 

 ternally, the upper part being pushed in towards the cranial cavity. 

 It is formed by the prootic anteriorly, by the exoccipital posteriorly, 

 and is completed by the cartilage lying between these bones. In 



