190 



MAMMALIAN ANATOMY 



THE SQUAMOUS PORTION. 



The squamous portion (Fig. 128) is a thin, vertical plate of bone, 

 about one-half longer than high, concave within and convex without. 

 The upper border is arcuate, and the lower border is almost straight. 

 It presents for examination an upper border and three surfaces, the 

 external, the internal, and the lower. 



FIG. 128. 



OUTER VIEW. 



INNER VIEW. 



POSITION OF SQUAMOUS. 



The upper border (Fig. 129) begins at the lower anterior angle, 

 runs upward and slightly forward for a short distance, then arches 

 upward and backward to reach the highest point at the junction of 

 the anterior and middle thirds of the bone. From this point it arches 

 downward with a less marked curvature, and just in front of the 

 posterior border of the bone it turns at almost a right angle sharply 

 upward and backward for a short distance, and terminates by forming 

 the anterior border of a narrow process, whereof the end is jagged and 

 the posterior border is parallel with the anterior and is continued 

 downward and forward as the prolongation of the lambdoidal ridge on 

 the occipital and separates the squamous from the mastoid. The free 

 border is thin and sharp ; for most of its length it is bevelled at the 

 expense of the internal surface and overlaps the sphenoid and parietal. 



The external surface is limited below bv a well-defined, shelf-like 



V 



ridge, which begins behind at the posterior limiting ridge and extends 

 almost straight forward, arching upward slightly above the external 

 auditory meatus, and is continued forward as the posterior and then 

 the upper border of the zygomatic process. It is known as the pos- 

 terior root of the zygomatic process. The surface is convex from before 

 backward in its anterior higher half, and concave in its posterior 

 half. The convexity is shorter and more marked below, just above 



