THE TEMPORAL BONE. 



35 



opening of the frontal sinus ; 15, placed near the inside of the roof of the orbit indicates 

 the inner ends of the ethmoidal or internal orbital foramina. 



Cerebral Surface. This surface forms a large concavity, but the roofs 

 of the orbital plates, which form its floor, are convex from side to side. 

 It is covered with digitate impressions, which, with the intervening ridges, 

 are strongly marked over the orbits. A groove, the sulcus frontalis, which 

 lodges the commencement of the longitudinal sinus, ascends in the middle 

 of the upper part of the bone ; its margins approach inferiorly, and are 

 elevated into a ridge, the crista frontalis. A small foramen, usually formed 

 in part by the central plate of the ethmoid, is situated at its base ; it is 

 known as the foramen ccecum, but transmits a minute vein from the nasal 

 fossae. This surface is bounded posteriorly by a thin linear border, which 

 articulates with the lesser wings of the sphenoid, and superiorly and 

 laterally by a serrated border, which articulates with the parietals, and 

 which, as has before been mentioned, slightly overlaps those bones above, 

 and is overlapped by them at the sides. 



THE TEMPORAL BONE. 



The temporal bone (os temporis) takes part in the construction of the 

 sifle and base of the skull, and contains in its interior the organ of hearing. 

 It is usually described in three parts, viz., an expanded anterior and superior 

 part the squamous portion, a much thicker posterior portion the mastoid, 

 and below and between these the petrous portion, a three-sided pyramid 

 exhibiting at its base externally the aperture of the ear and projecting 

 forwards and inwards into the base of the skull. 



It articulates posteriorly and internally with the occipital bone, superiorly 

 with the parietal, anteriorly with the sphenoid by the zygomatic process 

 with the malar, and by the glenoid cavity with the inferior maxillary bone. 



"$he SQUAMOUS PORTION extends forwards and upwards from its connection 

 with the other portions, and presents superiorly an arched border which 

 describes about two-thirds of a circle. 



Fi*. 32. 



Fig. 32. RIGHT TEMPO- 

 RAL BONE FROM THE 



OUTSIDE. | 



1, the external surface 

 of the squamous part ; 2, 

 the zygoma ; 3, the mas- 

 toid part ; 3 x , the mas- 

 toid process ; 4, the arti- 

 cular part of the glenoid 

 fossa ; 5, the articular 

 eminence at the root of the 

 zygoma, and above it the 

 tubercle ; 6, fissure of 

 Glaser ; 7, the tympanic 

 plate forming the posterior 

 non -articular part of the 

 glenoid fossa, terminating 

 behind in the vaginal pro- 

 cess ; 8, the meatus audi- 



torius externus ; 9, the 10 



auditory process ; 10, the 

 Btyloid process ; 13 x , the 

 mastoid foramen. 



The inner surface is marked by cerebral impressions, and by meningeal 

 grooves. At its npper border, the outer table is prolonged considerably 



