THE BULLA TYMPANICUM. 



185 



O. pmx., Os praemaxillare. Praemaxillary or intermaxillary bone. 



542. Prc. par., Processus paroccipitalis s. paramasioideus Paramastoid or 

 paroccipital process. This is a curved shelf-like projection of the exoccipital which abuts 

 against the caudal end of the bulla. 



Prc. pro., Processus mastoideus s. pars mastoidea. Mastoid portion of the peri- 

 oticum. 



Prc. z., Processus zygomaticus. Zygomatic process of the temporal bone. 



Prc. po., Processus postorbitale. Postorbital process of the frontal bone. 



543. Fig. 58 Preparation. The soft 

 parts were removed ; then, while the skull 

 was yet moist, the ventral face of the bulla 

 was ground off on a fine emery-stone. 

 It might be removed with a watch-spring 

 saw or on an ordinary grindstone. In 

 grinding, the pressure should be only 

 moderate to avoid breaking the delicate 

 septum. 



544. Bulla tympanica The auditory or tympanic 

 bulla. The bulla is a hollow subspherical part of the 

 0. tympanicum enclosing the tympanum or middle ear. 

 A delicate bony septum divides the cavity into two un- 

 equal parts. This septum arises from the floor, and 

 extends dorsad, but leaves a space over the fenestra ro- 

 tunda which puts the two chambers in communication. 



In the lateral aspect of the balla is the external auditory meat us (M. a. e.) ; attached to 

 the ectal part of this is the external ear, and to the ental part the Membrana tympani or 

 ear drum, which completely separates the tympanum or middle ear from the exterior of 

 the body. Flower, A, 110, and 26, 4 ; Huxley, B, 249 ; Straus-Durckheim, A, I, 409. 



Cd. oc., condylus occipitalis. Occipital condyle. 



545. Cn. eu., Canalis Eustachiana Eustachian canal. This is a short bony tube 

 leading from the tympanum to the ventral surface of the skull. Flower, A, 111. 



Fm. m., Foramen magnum, az. 



Fm. cd., Foramen condylare. Condylar foramen. 



Fm. ov., Foramen ovale. 



Fs. mnd., Fossa mandibularis. Mandibular or glenoid fossa (Fig. 57), 



Ft. rt., Fenestra rotunda (Fig. 57). 



Ft. ov., Fenestra ovalis. 



M. a. e., Meatus auditorius externus. External auditory meatus. 



O. boc., Os basioccipitale, az. Basioccipital bone. 



Prc. z., Processus zygomaticus. Zygomatic process of the temporal bone. 



Spt. tym., Septum tympanicum. The bony partition dividing the interior of the 

 bulla into two unequal chambers. 



546. Fig. 59 Preparation. The soft parts were removed 

 ( 250, B), and then the section was made with a watch-spring saw 

 while the skull was still moist. The section was made about 2 mm. 



FIG. 58. VENTRO - LATERAL 

 VIEW OF THE LEFT BULLA 

 AND ADJACENT PARTS ; x 1.5. 



