DEVELOPMENT OF THE EAR IN THE COMMON FROG. 1S3 



Fig. 10. Oblique transverse section through the head of a large 

 tadpole, just before the anterior legs are protruded. On 

 the left the first branchial cleft is shown, as well as the 

 opening of the Eustachian tube into the oesophagus. On 

 the right hand the centre of the eye is cut, and a section 

 of the Eustachian tube is shown considerably in front of 

 its point of origin from the throat : (x 10). 



Fig. 11. Section through the tympanic cavity and annular cartilage 

 in the same specimen. On the left it passes entirely in 

 front of the tympanic cavity, cutting the point of union 

 of the palatopterygoid bar with the trabeculae. The 

 section is completely in front of the eye : (x 12). 



Fig. 12. Diagrammatic sagittal section of a tailed frog on the left 

 side, showing the course of the Eustachian tube and the 

 position of the annular cartilage. It passes through the 

 ear and eye and the angle of the mouth. The greater 

 part of the length of the quadrate and palatopterygoid 

 cartilage is shown with the Meckelian cartilage below it, 

 as well as the outer portions of the hyoid and first three 

 branchial arches : (x 15). 



Fig. 13. Oblique section through the ear of the tadpole from which 

 Figs. 10 and 11 are taken. The columella is shown at 

 an early stage cut at two different levels. On the right 

 the interstapedial, and on the left the mesostapedial is 

 shown. The thymus lies a short distance to the outer 

 side of the columella : (x 10). 



Fig. 14. Diagrammatic horizontal section of a tailed frog, to show 

 the course of the columella. The eye is cut some distance 

 from its centre, and the anterior nares are included 

 in the section. The relations of the columella to the 

 auditory capsule, stapes, and thymus are shown : (X 15). 



Fig. 15. Oblique transverse section of a young frog's head, just after 

 the metamorphosis. The left side is more anterior than 

 the right. On the right the whole course of the columella 

 is shown ; it is as yet chondrified at its base alone. 

 Observe the fragmentary and asymmetrical condition of 

 the Kustnchiaii tube : (X 15). 



