

THE TEMPORAL BONE 



143 



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ingeal artery; (4) lateral to the hiatus, a smaller opening, occasionally seen, for 

 the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, 

 the termination of the carotid canal, the wall of which in this situation is deficient 

 in front; (6) above this canal the shallow trigeminal impression for the reception 

 of the semilunar ganglion. 



The posterior surface (Fig. 138) forms the front part of the posterior fossa of 

 the base of the skull, and is continuous with the inner surface of the mastoid 

 portion. Near the center is a large orifice, the internal acoustic meatus, the size of 

 which varies considerably; its margins are smooth and rounded, and it leads into 

 a short canal, about 1 cm. in length, which runs lateral ward. It transmits the 

 facial and acoustic nerves and the internal auditory branch of the basilar artery. 

 The lateral end of the canal is closed by a vertical plate, which is divided by a 

 horizontal crest, the crista falciformis, into two unequal portions (Fig. 140). Each 

 portion is further subdivided by a vertical ridge into an anterior and a posterior 

 part. In the portion beneath the crista falciformis are three sets of foramina; 

 one group, just below the posterior part of 

 the crest, situated in the area cribrosa media, 

 consists of several small openings for the 

 nerves to the saccule; below and behind this 

 area is the foramen singulare, or opening for 

 the nerve to the posterior semicircular duct; 

 in front of and below the first is the tractus 

 spiralis foraminosus, consisting of a number of 

 small spirally arranged openings, which encircle 

 the canalis centralis cochleae; these openings 

 together with this central canal transmit the 

 nerves to the cochlea. The portion above 

 the crista falciformis presents behind, the 

 area cribrosa superior, pierced by a series of 

 small openings, for the passage of the nerves 

 to the utricle and the superior and lateral 

 semicircular ducts, arid, in front, the area 

 faciauls, with one large opening, the com- 

 mencement of the canal for the facial nerve 

 (aquseductus Fallopii). Behind the internal 

 acoustic meatus is a small slit almost hidden 

 by a thin plate of bone, leading to a canal, 

 the aquseductus vestibuli, which transmits the 



ductus endolymphaticus together with a small artery and vein. Above and 

 between these two openings is an irregular depression which lodges a process of 

 the dura mater and transmits a small vein; in the infant this depression is repre- 

 sented by a large fossa, the subarcuate fossa, which extends backward as a blind 

 unnel under the superior semicircular canal. 



The inferior surface (Fig. 141) is rough and irregular, and forms part of the 

 exterior o*f the base of the skull. It presents eleven points for examination: (1) 

 near the apex is a rough surface, quadrilateral in form, which serves partly for the 

 attachment of the Levator veli palatini and the cartilaginous portion of the audi- 

 tory tube, and partly for connection with the basilar part of the occipital bone 

 through the intervention of some dense fibrous tissue; (2) behind this is the large 

 circular aperture of the carotid canal, which ascends at first vertically, and then, 

 making a bend, runs horizontally forward and medialward; it transmits into the 

 cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial 

 to the opening for the carotid canal and close to its posterior border, in front of the 

 jugular fossa, is a triangular depression; at the apex of this is a small opening, the 



FIG. 140. Diagrammatic view of the fundua 

 of the right internal acoustic meatus. (Testut.) 

 1. Crista falciformis. 2. Area facialis, with (2') 

 internal opening of the facial canal. 3. Ridge 

 separating the area facialis from the area crib- 

 rosa superior. 4. Area cribrosa superior, with 

 (4') openings for nerve filaments. 5. Anterior 

 inferior cribriform area, with (5') the tractus 

 spiralis foraminosus, and (5") the canalis cen- 

 tralis of the cochlea. 6. Ridge separating the 



"b- 

 (7') 

 Foramen 



tractus spiralis foraminosus from the area crib 

 rosa media. 7. Area cribrosa media, with (7' 

 orifices for nerves to saccule. 

 singulare. 



