426 



MANUAL OF ZOOLOGY 



the tympanic cavity (cav), which communicates with the 

 mouth by the short Eustachian tube already noticed (Fig. 

 251, ens. t), so that a probe thrust through the tympanic 

 membrane from outside passes directly into the mouth. In 



-MP 



tfZT— A\ 

 ZXJ7— ee 



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

 optic chiasma; HH, cerebellum; Hyp, pituitary body: Inf, infundibulurn; 

 L. ol, olfactory lobe; Med, spinal cord; MH, midbrain; A'//, medulla ob- 

 longata; Th. opt, optic thalamus; TV. opt, optic tract; '"//, cerebral hemi- 

 sphere; ZH, diencephalon ; / — X, cerebral nerves; Xlf. (/), 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 



