184 FRANCIS VILLY. 



Fig. 16. Section similar to the last, but through an older frog. The 

 columella is now chondrified throughout. Observe that 

 the Eustachian tube is complete on the left, but frag- 

 mentary on the right : ( x 15). 



Fig. 17. Diagrammatic transverse section of an adult frog's head. 

 The whole course of the recessus is shown, with the con- 

 nection between the two sides, both above and below the 

 brain. On the right as much of the columella is shown 

 as possible, and the whole course of the Eustachian tube 

 is represented. The anterior parts of the sternum and 

 thymus are cut, and the anterior cornu of the hyoid is 

 shown at different levels on the two sides : ( x 8). 



Fig. 18. Diagrammatic horizontal section of an adult frog's head. 

 The length of the recessus is shown on the right, and the 

 columella and stapes are in position. On the left an 

 attempt has been made to show the distribution of the 

 auditory nerve to the various parts of the ear. The 

 nerve bifurcates within the skull, and the anterior branch 

 supplies the sacculus, the utriculus, and the two anterior 

 ampullse. The posterior branch runs to the three parts 

 of the cochlea and to the posterior ampulla. On the 

 right the two perilymphatic canals are seen. Besides 

 the parts mentioned, the section cuts the centre of the 

 eye and of the cerebral hemispheres, the lower part of the 

 optic lobes, the nose, and the G-asserian ganglion : (x 8). 



Fig. 19. Diagrammatic transverse section through the posterior part 

 of an adult frog's ear, to show the course of the peri- 

 lymphatic canals. In this figure the whole of the pectoral 

 arch is shown, along with the head of the humerus. The 

 posterior part of the stapes appears, as do the posterior 

 vertical and the horizontal canal (cut twice), the posterior 

 ampulla, and the two parts of the cochlea concerned. 

 The brain is cut through the anterior part of the medulla 

 oblongata, and the choroid plexus is shown : (x 8). 



