42 THE BONES. 



Faces. The external face is convex, and marked by some muscular 

 imprints, vascular fissures, and openings which penetrate the parieto- 

 temporal canal. It forms part of the temporal fossa, and gives origin near 

 its middle to the zygomatic process, a long eminence which at first, runs 

 outwards, and soon curves forwards and downwards to terminate in a 

 thin summit. The base of this eminence forms, in front, a concave surface 

 belonging to the temporal fossa ; behind, it offers the articular surface which 

 corresponds with the maxillary bone. The latter is composed of : 1, A condyle 

 transversely elongated, convex above and below, and slightly concave from 

 side to side ; 2, A glenoid cavity, limited below by the condyle, above by a 

 mammiform eminence, the supercundyloid, 1 against which rests the maxillary 

 condyle when this bone is drawn backwards ; it is immediately above this 

 eminence that the inferior orifice of the parieto-temporal canal opens. The 

 external face of the zygomatic process is smooth and convex ; the internal, 

 concave, is also smooth, and bordered outwards by the temporal fossa. Its 

 anterior border is sharp and convex ; the posterior, very short, is thick and 

 roughened. Its summit is flattened from before to behind, and marked by 

 notches on its two faces; it somewhat resembles a wedge, fixed as it is 

 between the orbital process of the frontal bone and the zygoma ; it comes 

 in contact with the maxillary bone, and by a small portion of its anterior 

 face, which is deprived of notches, it concurs in circumscribing the orbital 

 cavity. In the domesticated animals, as in Man, the zygomatic process 

 appears to arise from the surface of the bone by two roots : one, the inferior 

 or transverse, is represented by the condyle ; the other, the superior, forms a 

 sharp crest which is continuous with the anterior border of the process, and 

 above, joins the lateral crest of the occipital protuberance. 



The internal or cerebral face of the squamous portion is divided into two 

 parts by an almost vertical channel which terminates above the super- 

 condyloid eminence, and which, meeting a similar furrow on the parietal 

 bone, forms the parieto-temporal canal. The superior portion is but of 

 small extent, and of a triangular form ; it articulates by a simple harmonia 

 suture with the external face of the -petrous portion. The inferior part, the 

 widest, presents in its middle some cerebral impressions. For the re- 

 mainder of its extent or circumference, it is cut into a wide, dentated, and 

 lamellar bevel, which brings it in contact with the surrounding bones. 



Circumference. This may be divided into two borders : one, anterior, is 

 convex and united with the parietal and frontal bones ; the other, posterior, 

 articulates with the sphenoid in its inferior moiety, and is provided, above 

 the level of the supra-condyloid eminence, with a deep notch which receives 

 the external auditory canal. Superiorly, the two borders unite at the summit 

 in a thin point which rests on the occipital bone. 



Structure. The squamous portion of the temporal bone is formed of 

 two very thin compact plates which have but little spongy tissue between 

 them ; the latter, however, is very abundant in the body of the zygomatic 

 process. 



Development. It is developed from a single nucleus of ossification. 



TUBEROUS PORTION. This is one of the most interesting parts of the 

 skeleton for study, in consequence of its containing two systems of cavities 

 which inclose the essential organs of hearing. One of these systems is 

 named the cavity of the tympanum or middle ear ; the other forms the internal 

 ear. These cavities will be studied when we come to speak of the auditory 



1 In Man this is represented by the inferior or vertical ramus of the upper root of tho 

 zygomatic process. 



