58 



THE SKELETOX OF THE FROG. 



iii. The dentary is a flat bone covering the outer sur- 

 face of the distal half of Meckel's cartilage, as far 

 forward as the mentonaeckelian bone. 



iv. The mentomeckelian is a small ossification in 

 Meckel's 'cartilage at the symphysis, i.e., the 

 union of the arches of the two sides at the chin. 



FP X K M 



Fig. 11. A transverse section across the posterior jiart of the frog's 

 head, to show the position and relations of the auditory organs, 

 Eustachian tubes, and hyoid apparatus. On the right side the section 

 passes through the tympanic cavity and the cohimella ; on the left side 

 through the anterior cornu of the hyoid. The cartilage is dotted, and 

 the bones, except the columella, are represented black. 



A, parasi)henoid : AS, angulosplenial : B, buccal cavity : C, columella : 

 D, tymi)anic membrane : E, Eustachian tube : F, anterior cornu of the 

 hyoid : FP, frontoparietal : G, glottis : H, arytenoid cartilage : I, posterior 

 cornu of hyoid : K, auditory nerve : L, vestibule : M, anterior vertical 

 semicircvilar canal : N, horizontal semicircular canal : O, pro-otic : 

 P, pterygoid : Q, quadrate cartilage : R, quadratojugal : S, squamosal : 

 T, annulus tympanicus : V, vocal cord : X, mid-brain. 



4. The Hyoid Apparatus (Fig. 10). This consists of the 

 hyoidean arch and the remains of the branchial arches 

 of the two sides, together with a median ventral 

 plate, the body of the hyoid, which unites their 

 lower ends together, and lies in the floor of the mouth. 

 The hyoid apparatus consists almost entirely of 

 cartilage. 



a. The hyoid arch. 



i. The columella (Figs. 10 and 11) is formed from the 

 top of the hyoid arch : it is a small rod, partly 



