426 



MANUAL OF ZOOLOGY 



SECT. 



the tympanic cavity {cav), which communicates with the 

 mouth by the short Eustachian tube already noticed (Fig. 

 251, eus. /), so that a probe thrust through the tympanic 

 membrane from outside passes directly into the mouth. In 



ftfVil 

 ff } 1 



E 



-MR 



-M.d) 



FIG. 255. Rana esculenta. The brain. A, from above; B, from below, ch. opt, 

 optic chiasma; HH, cerebellum; Hyp, pituitary body; //, infundibulum; 

 L. ol, olfactory lobe; Med, spinal cord; MH, mid brain; NH, medulla ob- 

 longata; Th. opt, optic thalamus; Tr. opt, optic tract; I'H, cerebral hemi- 

 sphere; ZH, diencephalon ; IX, cerebral nerves; XII. (/), hypoglossal (first 

 spinal) nerve. (From Wiedersheim's Comparative Anatomy} 



the roof of the tympanic cavity lies a slender rod of bone 

 and cartilage, the columella, its head, or extra-columella, 

 attached to the inner surface of the tympanic membrane, its 



