THE SKULL. 3r 
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 (a), petrous (4), and tympanic (c) portions of the 
temporal bone. 
Fic. 22.TEMPORAL BONE, EXTERNAL Fic. 23.—TEMPORAL BoNE, INTERNAL 
SURFACE. SURFACE. 
a, squamous portion; 4, petrous portion; ¢, ¢, tympanic portion (c¢, entotym- 
panic; ¢’, ectotympanic); d@, zygomatic process; e, mastoid portion of the petrous; 
J; mandibular fossa; g, postmandibular process; #, tuberculum articulare; 7, ex- 
ternal auditory meatus; 7, stylomastoid foramen; %, pit for tympanohyal bone; 
2, mastoid process; #, grooves bounding the jugular foramen; #, internal auditory 
meatus; v, appendicular fossa; Z, hiatus facialis; g, styliform process of tympanic 
bulla. 
The squamous portion (2) (squama temporalis) is thin and 
oval or has the form of an equilateral triangle with rounded 
angles, with a curved process, the zygomatic process (2), 
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 bevelledand 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 
