THE TEMPORAL BONE 



71 



The anterior, continuous with the lower border, is short, broad, convex, and directed 

 medialh- to terminate in the articular tubercle, which is covered with cartilage in the recent 

 state, for articulation with the condyle of the lower jaw. The middle root, sometimes very 

 prominent, forms the post-glenoid process. It separates the articular portion of the man- 

 dibular fossa from the external auditory meatus and is situated immediately in front of the 

 petro -tympanic (Glaserian) fissure. The posterior root, prolonged from the upper border, is 

 strongly marked and extends backward as a ridge above the external auditory meatus. It is 

 called the temporal ridge (supra-mastoid crest), and marks the arbitrary line of division be- 

 tween the squamous and mastoid portions of the adult bone. It forms part of the posterior 

 boundary of the temporal fossa, from which, as well as from the ridge, fibres of the temporal 

 muscle arise. Where the anterior root joins the zygomatic process is a slight tubercle — the 

 preglenoid tubercle — for the attachment of the temporo-mandibular ligament, and between the 

 anterior and middle roots is a deep oval depression, forming the part of the mandibular fossa 

 for the condyle of the lower jaw. The mandibular fossa is a considerable hollow, bounded in 

 front by the articular tubercle and behind by the tympanic plate which separates it from the 

 external auditory meatus. It is divided into two parts by a narrow slit — the petro-tympanic 

 (Glaserian) fissure. The anterior part [fades articularis], which belongs to the squamous 

 portion, is articular, and, like the articular tubercle, is coated with cartilage. The posterior 



Fig. 93. — The Left Temporal Bone. (Seen from the inner side and above.) 



Squamous portion 



Meningeal groove 







Zygomatic process 



Petro-squamous 

 fissure 



Eminentia arcuata 



Superior petrosal 

 sulcus 



Sigmoid groove 



Mastoid foramen 



Masseter 

 — Hiatus canalis facialis 



Internal auditory meatus 



— Stylo-pharyngeus 



Aqusductus vestibuli 



Fossa subf rcuata 



Mastoid process Aquseductus cochleae 



Styloid process 



part, formed hy the tympanic plate, is non-articular and lodges a lobe of the parotid gland. 

 Immediately in front of the articular tubercle is a small triangular surface which enters into 

 the formation of the roof of the zygomatic fossa. 



The inner or cerebral surface "of the squamous portion is marked by furrows for the con- 

 volutions of the brain and grooves for the middle meningeal vessels. At the upper part of the 

 surface the inner table is deficient and the outer table is prolonged some distance upward, 

 forming a thin scale, with the bevelled surface looking inward to overlap the corresponding 

 edge of the parietal. Anteriorly the border is thicker, serrated, and slightly bevelled on the 

 outer side for articulation with the posterior border of the great wing of the sphenoid. Pos- 

 teriorly it joins the rough serrated margin of the mastoid portion to form the parietal notch. 

 The line separating the squamous from the petrous portion is indicated at the lower part of 

 the inner surface by a narrow cleft, the internal petro-squamous suture, the appearance of 

 which varies in different bones according to the degree of persistence of the original line of 

 divi.sion. 



The mastoid portion [pars mastoidea] is rough and convex. It is bounded 

 aboA-e by the temporal ridge and the parieto-mastoid suture; in front, by the 

 external auditory meatus and the tympano -mastoid fissure; and behind, by the 

 suture between the mastoid and occipital. As already pointed out, it is formed 

 by the squamous portion in front and by the base of the petrosal behind, the 

 line of junction of the two component parts being indicated on the outer surface 

 by the external petro-squamous suture (squamo-mastoid). The appearance of 

 the suture varies, being in some bones scarcely distinguishable, in others, a series 



