XIII 



PHYLUM CHORDATA 



529 



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

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

 and greatly arched 

 outwards. The 

 noid cavity is 



form of a 

 groove, to 



gle- 

 in the 

 transverse 

 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 

 the auditory ossicles 

 and the opening of the 

 Eustachian tube ; the 

 bony auditory meatus 

 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 



P 



Jm 



oo 



FIG. 1179. Section of the left auditory bulla of Tiger (Felis 

 tigris). * aperture of communication between the two 

 chambers into which the cavity of the bulla is divided ; 

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

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

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

 chambers; Sq. squamosal. (After Flower.) 



FIQ. 1180. Lateral view of skull of Dog (Canis familiaris). 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 ; ^V. nasal ; P. parietal ; Pal. palatine ; 

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

 Sg. 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. 



