xin 



PHYLUM CHORDATA 



529 



the different groups ; in the Bears and their allies, and in the Dogs, 

 it is elongated ; in the Cats it is x very short. The zygoma is strong 

 and greatly arched 

 outwards. The gle- 

 noid cavity is in the 

 form of a transverse 

 groove, to the shape 

 of which the trans- 

 versely elongated con- 

 dyle is adapted. In 

 the Cats there is a 

 large rounded tym- 

 panic bulla (Fig. 1179), 

 the cavity of which is 

 divided into two parts 

 anterior and pos- 

 terior by a septum, 

 the anterior containing 



anrli+nrv nQnrlp FlG / 1179. Section of the left auditory bulla of Tiger (Felis 



i d/utllUUiy tigris). * aperture of communication between the two 



anrl thp nnpnincr nf tViP chambers into which the cavity of the bulla is divided ; 



a. m. external auditory meatus; BO. basi-occipital ; e. 



Eustachian tube ; the Eustachian tube ; ic. the inner chamber ; oc. the outer 



j'. chamber; Pt. periotic ; s. septum between the two 



DOny auditory meatUS chambers ; Sq. squamosal. (After Flower.) 



is short : the parocci- 



pital is closely applied to the posterior surface of the tympanic 

 bulla. In the Dogs the septum of the bulla is incomplete, the 

 auditory meatus short, and the paroccipital process not applied 



oo 



Jni 



g.cca 



C.occ. 



FIG. 1180. Lateral view of skull of Dog (Canis familiar is). C. occ. occipital condyle ; F. 

 frontal ; F.inf. infra-orbital foramen ; Jg. jugal ; Jm. premaxilla ; L. lacrymal ; M . Maxilla ; 

 Maud, external auditory meatus ; Md. mandible ; N. nasal ; P. parietal ; Pal. palatine ; 

 Pjt. zygomatic process of squamosal ; Pt. pterygoid ; Sph. ali-sphenoid ; Sq. squamosal ; 

 Sq. occ. supra -occiptial ; T. tympanic. (From Wiedersheim's Comparative Anatomy.) 



to the bulla. In the Bears and their allies (Fig. 1181) the bulla is 

 usually less dilated, and the septum is absent or only represented 

 by a ridge, while the bony auditory meatus is elongated. 



