132 



OSTEOLOGY. 



facial canal. Reaching forwards, it extends to the apex of the petrous part ; whilst 



laterally it forms part of the medial wall of the tympanum, surrounds the fenestra vesti- 



buli, and encloses within its substance portions of the cochlea, 



vestibule, and superior semicircular canal. Another centre, the 



Opisthotic, appears in the vicinity of the promontory on the 



medial wall of the tympanum, surrounds the fenestra cochleae, 



forms the floor of the vestibule, and extends medially to complete 



the floor of the internal acoustic meatus. Surrounding the cochlea 



inferiorly and laterally, it completes the floor of the tympanum, 



and ultimately blends with the anterior and inferior part of the 



tympanic ring. The carotid 



Canal at first grooves it, and is Lateral semicircular canal 



then subsequently surrounded 

 by it. According to Lambertz 

 the lamina spiralis of the cochlea 

 ossifies in membrane. The roof 

 of the tympanum is formed from 

 a separate centre, the Pterotic, 

 which extends backwards to- 

 wards the superior semicircular 

 canal, and encloses the tympanic 

 part of the facial canal ; later- 

 ally this centre unites by suture 

 with the squamosal, and sends 

 down a thin process, which ap- 

 pears between the lips of the 

 petro - tympanic fissure, and 

 forms the lateral wall of the 

 auditory tube. Nuclei, either 

 single or multiple, Epiotic, appear 



Superior semicircular 

 canal 



Vestibule into 



openings of 



semicircular canals 



Internal 

 acoustic meatus 



Fenestra vesti- 

 buli cut across 



Fenestra cochleae 

 cut across 



Opening leading 

 into tympanic 

 antrum 



Canalis facialis 

 Canalis stapedii 



Tympanum 



External 

 acoustic meatus 



FIG. 141. VERTICAL TRANSVERSE SECTION THROUGH THE LEFT 

 TEMPORAL BONE (Posterior Half of Section). 



in the base of the 



Osseous part or'the auditory tube 



Styloid process 

 broken off 



Mandibular 



petrous part, and envelop the 

 posterior and lateral semi- 

 circular canals. It is by ex- 

 tension from this part that 

 the mastoid process is ulti- 

 mately developed. The 

 styloid process, an inde- 

 pendent development from 

 the upper end of the carti- 

 lage of the second visceral 

 arch, is ossified from two 

 centres. The upper or basal 

 appears before birth, and 

 rapidly unites with the petro- 

 mastoid, the tympanic plate 

 internal acoustic encircling it in front. This 

 meatus represents the tympanohyal 



of comparative anatomy. At 

 birth, or subsequent to it, 

 another centre appears in the 

 cartilage below the above : 

 this is the stylohyal. Anky- 

 losis usually occurs in adult 

 life between the tympanohyal 

 and stylohyal, the union of 

 the two constituting the so- 

 called styloid process of 

 human anatomy. 



The centre from which the 

 squamo-zygomatic develops 

 appears in membrane about 

 the end of the second month. Situated near the root of the zygoma, it extends forwards 

 and laterally into that process, medially to form the floor of the infra-temporal fossa, and 

 upwards into the squamosal. From this latter there is a downward and backward exten- 



Groove for 



membrana 



tympani 



External 



acoustic 



meatus 



Mastoid air-cells - 



Carotid canal 



Tympanum 



Cochlea 



Vestibule, fenestra 

 vestibuli cut across 



Superior semicircular 



canal 



Canalis facialis 



Lateral semicircular canal 



Fia. 142. HORIZONTAL SECTION THROUGH THE LEFT TEMPORAL BONE 

 (Lower Half of Section). 



