64 THE CAT. [CHAP. m. 



upper surface, as an undulating plate (concave externally in front, 

 and convex behind) with a crescentic inferior margin. The hinder, 

 externally convex, part of this plate forms part of the temporal 

 fossa; the anterior, externally concave, part of it forms the inner 

 wall of the orbit, and (towards its front end) the outer wall of the 

 nasal cavity. 



Viewed internally, each frontal shows above, a flattened surface (/) 

 for junction with its fellow of the opposite side ; behind this is a 

 deep concavity for part of the brain, and in front, a flattened and 

 irregularly roughened surface (fa) the outer wall of the hinder 

 part of the nasal cavity. 



Thus, the two frontals together have, when viewed from below, 

 somewhat the figure of a bisected hour-glass. There is, behind, a 

 large conical cavity (with the apex forwards) for the brain, while 

 in front is a smaller conical cavity (with the apex backwards) the 

 nasal chamber. Consequently, when the two frontals are seen together 

 from behind, they exhibit a deep median notch, open below, indi- 

 cating the point of communication between the anterior and posterior 

 conical cavities just mentioned, and situated at the point where each 

 frontal is laterally constricted. This notch, in the perfect skull, is 

 filled up by a bone called the ethmoid, which forms the hinder end 

 of the nasal chamber. At its anterior end, each frontal bifurcates 

 laterally into a sharp pointed "nasal process" (m) and a more obtuse 

 " pre-orbital process " (p). Between these processes each frontal 

 receives an ascending process of the maxillary bone. While the 

 two nasal bones are received between the slightly diverging nasal 

 processes of the two frontal bones (see Fig. 28). 



Within the substance of the middle upper part of the bone is a 

 cavity, more or less filled with air, called the frontal sinus, which 

 cavity is prolonged out into the post-orbital process. 



The frontals articulate behind, with the parietals ; laterally, with 

 the orbito- and ali-sphenoids, and sometimes also with the temporals ; 

 below with the palatines, the maxillaries, the ethmoid, and the lachry- 

 mals ; in front, with the maxillaries and nasals. 



26. On each side of the hinder part and base of the cranium 

 we find an exceedingly complex bone, called the TEMPORAL. When 

 looked at externally it exhibits a very conspicuous oval opening (the 

 meatus auditonus externus), which is the aperture (me) leading from 

 without to the internal ear. From in front of this a bar of bone, 

 the zygom'atic process (s), arches horizontally forwards and outwards, 

 and contributes, with the large plate of bone above it(-s^), the 

 squamous element of the temporal bone, or the " squamosal." This 

 bony plate is convex without and concave within, and with a very 

 rounded superior margin, which overlaps the lower part of the out- 

 side of the parietal bone above. 



The zygomatic process is somewhat arched vertically, and is bevelled 

 off at its distal end, which lies upon the malar bone. At its hinder 

 end this process has beneath an elongated surface, concave from 

 before backwards, and termed the glcnoid surface (</). 



