THE SKULL. 31 



up of three portions which are distinct in kittens but somewhat 

 firmly united in adult cats. In lower vertebrates these portions 

 are distinct bones called the Squamous, the Petrous, and the 

 Tympanic bones. In the cat they may be described as the 

 squamous (), petrous (), and tympanic (c] portions of the 

 temporal bone. 



*q" '^a^^jjjP' 



p ' m 



FIG. 22. TEMPORAL BONE, EXTERNAL FIG. 23. TEMPORAL BONE, INTERNAL 

 SURFACE. SURFACE. 



fl, squamous portion; 6, petrous portion; f, c", tympanic portion (c, entotym- 

 panic; c', ectotympanic); </, zygomatic process; e, mastoid portion of the petrous; 

 y, mandibular fossa; g, postmandibular process; /i, tuberculum articulare; i, ex- 

 ternal auditory meatus;y, stylomastoid foramen; k, pit for tympanohyal bone; 

 /, mastoid process; m, grooves bounding the jugular foramen; n, internal auditory 

 meatus; o, appendicular fossa; /, hiatus facialis; g, styliform process of tympanic 

 bulla. 



The squamous portion (a) (squama temporalis) is thin and 

 oval or has the form of an equilateral triangle with rounded 

 angles, with a curved process, the zygomatic process (*/), 

 arising from its ventral border. Its outer surface (Fig. 22) is 

 convex and smooth and gives origin to part of the temporal 

 muscle. Its inner surface (Fig. 23) is concave and smooth 

 except near the margins, where it is bevelled and rough. The 

 roughened border is broader dorsad and caudad. The ventral 

 margin of the bone is turned mediad at its cranial end so that 

 the lateral face of the inverted portion looks ventrad. By this 

 portion of its lateral face the squamous rests upon the tympanic 

 bulla, and its edge articulates with the tentorium and the wing 

 of the sphenoid. The remaining (caudal) portion of the ventral 

 border overlies the mastoid portion (<?) of the petrous. By the 

 remainder of its border the bone articulates with the parietal 

 dorsad and with the wing of the sphenoid craniad. The 



