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 



ZE- 

 ZB Tr.opl. 



-MH 



J "f-i 



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

 optic chiasm a; HH , cerebellum ; HyP, pituitary body ; Inf, infundibulum ; 

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

 longata; Th. opt, optic thalamus; 7V. opt, optic tract; I'H, cerebral hemi- 

 sphere; ZH, diencephalon ; / — .-V, 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 



