THE TEMPORAL BONE 



85 



the middle meningeal artery. (4) A smaller opening (apertura superior canalicnli 

 tympanici}, occasionally seen external to the latter, for the passage of the smaller 

 petrosal nerve. (5) Near the apex of the bone, the termination of the carotid 

 canal (foramen caroticum internum), the wall of which in this situation is deficient 

 in front. (6) Above the canal a shallow depression, the trigeminal depression 

 (imprcssio triycmini], for the reception of the Gasserian ganglion. 



The anterior or tympanic surface is hidden by the tympanic portion of the bone, 

 and is best studied either in very young skulls or in bones which have been cut 

 internal to the tympanic membrane. This surface forms the postero-internal 

 wall of the tympanum and presents an oval foramen (fenestra ovalis s. vestibuli}, 

 into which the base of the stapes is fitted. Just above and posterior to the fenestra 

 ovalis is the mastoid antrum, leading from the tympanum to the mastoid cells. 

 The antrum is roofed by the tegmen tym- 



pani. Below and internal to the fenestra 2 3 



ovalis is a rounded eminence, the promon- 

 tory, formed by the first turn of the cochlea. 

 Below the promontory is situated the fen- 

 estra rotunda, which is closed in the recent 

 state by a membrane. 



Above and internal to the fenestra ovalis 

 is the orifice of the canal which transmits 

 the Tensor tympani; below this is the 

 Eustachian canal for the passage of air 

 from the pharynx to the tympanum. The 

 two canals are separated by the processus 

 cochleariformis. 



The posterior surface forms the front part 

 of the posterior fossa of the skull, and is 

 continuous with the inner surface of the 

 mastoid portion of the bone. It presents 

 three points for examination: (1) About 

 its centre a large orifice, the meatus audi- 

 torius internus (meatus acusticus interims), 

 which varies considerably in size; its margins 

 are smooth and rounded, and it leads into a 

 short canal, about one-third inch in length, 

 which runs directly outward and is closed by 

 a vertical plate, the lamina cribrosa, which is divided by a horizontal crest, the 

 falciform crest (crista falciformis), into two unequal portions (Fig. 51). Each 

 portion is subdivided by a small vertical crest into two parts, named, respectively, 

 anterior and posterior. The lower portion presents three sets of foramina: 

 one group just below the posterior part of the crest, the area cribrosa media, con- 

 sisting of a number of small openings for the nerves of the saccule; below and 

 posterior to this, the foramen singulare, or opening for the nerve of the posterior 

 semicircular canal; in front and below the first, the tractus spiralis foraminosus, 

 consisting of a number of small, spirally arranged openings which terminate 

 in the canalis centralis cochleae and transmit the nerve of the cochlea; the upper 

 portion, that above the crista, presents behind a series of small openings, the 

 area cribrosa superior, for the passage of filaments of the utricle and superior and 

 external semicircular canal, and, in front, one large opening, the commencement 

 of the aquaeductus Fallopii (canalis facialis], for the passage of the facial nerve. 

 (2) Behind the meatus auditorius is a small slit (apertura eoderna aquaeductus 

 vestibuli}, almost hidden by a thin plate of bone, leading to a canal, the aquae- 

 ductus vestibuli, which transmits the ductus endolymphaticus, together with a small 



FIG. 51. Diagrammatic view of the fundus of 

 the internal auditory meatus : 1. Falciform crest. 

 2. Anterior superior cribriform area. 1' ' . Internal 

 opening of the aquaeductus Fallopii. 3. Vertical 

 crest which separates the anterior and posterior 

 superior cribriform areas. 4. Posterior superior 

 cribriform area, with (4') openings for nerve 

 filaments. 5. Anterior inferior cribriform area. 

 5'. Spirally arranged, sieve-like openings for the 

 nerves to the cochlea. 5". Opening of the cen- 

 tral canal of the cochlea. 6. Crest which sepa- 

 rates the anterior and posterior inferior cribriform 

 areas. 7. Posterior inferior cribriform area. 7'. 

 Orifices for the branches of the nerve to the 

 saccule. 8. Foramen singulare of Morgagni, 

 with the anterior portion of the canal which gives 

 passage to the nerve to the posterior semicircular 

 canal. (Testut.) 



