THE TEMPORAL BONES 



THE TEMPORAL BONES 



The adult temporal bone consist*; of three })arts, so firmly united as to afford 

 little trace of its complex origin. At Inrth the three parts are easily separable as 

 the squamosal, petrosal, and tympanic. 



Tlu' squamosal resembles a large scale; it is attached at right angles to thf 

 petrosal, and furuis part of the side wall of the skull. It is thin, and in i)lact*s 

 translucent. The outer surface is smooth and forms part of the temporal fossa; it 

 presents one, and occasionally two nearly vertical grooves for the deep temporal 

 arteries. A ridge of bone, the supra-mastoid crest, runs immediately above the 

 external auditory meatus, and is continued onwards to the zygoma. 



The zygoma is a narrow projecting bar of bone, jutting forwards and lying 

 parallel witli the squamosal* It has two surfaces and two borflers. The outer 

 surface is subcutaneous; the inner looks towards the temporal fossa. The inner 

 surface and lower border give origin to the masseter muscle. The upper border 

 receives the temporal fascia. The tip of the zygoma is serrated for articulation 

 with the malar. Posteriorly, tlie lower border ends in a tubercle, which is the 

 meeting point of two ridges; of these, the anterior passes inwards at right angles 

 to the zygoma, and expands into the articular eminence which serves as an 



Fi(i. 4;i.— Thk Left Temporal Bone. lOuter view.) 



ZYGOMATIC TUBERCLE 



GLENOID FOSSA 



GLASERIAN FISSURE 



TYMPANIC PLATE 



STYLOID PROCESS 



TEMPORAL FOSSA 

 POST-GLENOiO TUBERCLE 

 AUDITORY MEATUS 



AURICULAR FISSURE 



articular facet for the condyle of the mandilile when the mouth is opened. The 

 second ridge runs 1)ackwards and forms the upper boundary of the glenoid fossa, 

 and curving downwards ends in a tubercle, the post-glenoid tubercle, immediatt4y 

 anterior to tlie Glaserian fissure. The oval dee}j depression between these ridges 

 is the glenoid fossa, which receives the condyle of the mandible. This fossa is 

 limited posteriorly l»y the Glaserian fissure. 



The inner surface of the squamosal presents furrows for the convolutions of 

 the l»rain and grooves for the middle meningeal arteries. The line of union between 

 the squamosal and petrosal is sometimes indicated ])ya persistent petro-squamosal 

 suture. Rarely the two portions remain permanently separate. 



The superior Ixmler of the squamosal is thin, and bevelled on the cerel)ral 

 surface where it overlaps the parietal; anteriorly it is serrate(l for the ))osterior 

 border of the greater wing of the sphenoid. Posteriorly it joins the rough serrated 

 margin of the petrosal to form the i)arietal notch. 



The petrosal element is a four-sided pyramid of very dense bone; its base is 

 formed Ijy the mastoid process; the apex is rough and forms part of the boundary 

 of the foramen lacerum medium. Two sides of the pyramid j^roject into the cranial 

 cavity, of which one fonns the j)Osterior boundary of the middle fossa, and the 

 other the anterior boundary of the ])Osterior fossa of the cranium. Of the two 

 remaining surfaces, one a])pears on the under surface iif the skull, and the fourth 

 constitutes the inner wall of the recess called the tynqianum. 



