Ill 



TYMPANIC CAVITY 



45 



bony rods which pass backwards, diverging as they go, 

 one on either side of the glottis. 



Two apparently insignificant structures connected 

 with the skull must be described because of their con- 

 nection with the organ of hearing. Behind the suspen- 

 sorium is a recess, roofed over by the squamosal, and, 

 in the entire frog, converted by muscle and other tissues 



Trternb.Lab 



ctntymp 



lymp.cciv 

 mp.TneTnb 



o.st 



FIG. 10. Transverse section (diagrammatic) through the head of a Frog at the 

 level of the tympanic cavity. The various parts of the skull shown in section are 

 black, the muscles, &c., grey, and the skin and mucous membrane white. ( X 5.) 

 an. tytnp. tympanic ring ; t. hy. body of hyoid ; buc. cav. cavity of pharynx ; 

 ch. plx. choroid plexus ; col. columella ; eus. t. Eustachian tube ; fen. ov. 

 fenestraovalis ; med. obi. medulla oblongata ; memb. lab. membranous labyrinth ; 

 mnd. mandible ; Nv. VIII. auditory nerve ; o. st. omosternum ; pig. pterygoid ; 

 qu. jn. quadrato-jugal ; stp. stapes ; tymp. cav. tympanic cavity ; tymp. 

 memb. tympanic membrane. (From Parker and Haswell's Zoology.) 



into a chamber, the tympanic cavity (Fig. 10, tymp. cav), 

 bounded externally by the tympanic membrane, and 

 communicating with the mouth by the Eustachian tube. 

 Supporting the tympanic membrane, as the frame of 

 a tambourine supports the parchment, is a cartilaginous 

 ring, the tympanic ring (an. tymp, shown in section). 

 Stretching across the tympanic cavity from the 

 outer wall of the auditory capsule to the tympanic 



