620 



B. r. Kingsbury and II. D. Keed. 



These connections appear to be an adaptation to the babits and 

 environment of the animal. During larval life and in such forms 

 as Necturus and Cryptobranchus the body is either supported by 

 water, or rests full length upon the bottom or some submerged object, 

 the arms and legs playing a small part, if any, in its support. The 

 primitive connections of the columella here persist and function as 

 the transmission line between the exterior and the inner ear. Some 

 evidence for this view is found in certain Anurans. In Pelobates 

 there is no tympanic cavity, and the eustachian tube is much reduced. 

 The fenestral plate in this form is connected by strong ligament 



Fig. 21b. Same as Fig. 21a, for terrestrial forms. Col., columella; H.a., 

 hyoid arch ; L.s-c, ligameutum squamoso-columellare ; M.op., musculus oper- 

 cularis ; M.I., skeleton of lower jaw ; Op., operculum ; Pq., palatoquadratum ; 

 8q., OS squamosum ; S.s., suprascapula ; St.C, stilus columellae. 



with the squamosum. Similar conditions obtain in Bombinator, 

 excepting that the fenestral plate is connected with the hyoid. In 

 either case the inner ear is placed in communication with the exterior 

 through the floor of the mouth. It is interesting to note in this 

 connection that Pelobates is a thoroughly burrowing form while 

 Bombinator is just as thoroughly an aquatic one. 



In the urodele Siren, where the usual skeletal connections of 

 the fenestral plate are wanting, they seem to be compensated for by 

 the attachment of the stilus columellae to the hyoid by means of the 

 strong hyo-columellar ligament. 



When terrestrial life is assumed the body is more or less supported 



