On the Perilymphatic Spaces of the Amphibian Ear. 245 



brane related to it contains the pars interna columellae, forming a 

 "pseudoperculum". Owing to the fact that the perilymphatic space 

 passes out through the fenestra vestibuli, the membrane of this aper- 

 ture and the aperture itself are not coextensive. The membrane (with 

 its enclosed cartilages) forms part of the wall of a space (fossa fenestrae 

 vestibuli) opening into the auditory capsule through the fenestra vesti- 

 buli. The arrangement is perhaps of importance in lessening the effect 

 of violent shocks imparted to the membrane. 



IV. Discussion of Results, with a theory as to the origin of the 

 Fenestra vestibuli (fenestra ovalis). 



From the foregoing it will be realized that the perilymphatic spaces 

 are probably not only of great physiological importance, but have also 

 had considerable influence on the disposition of the skeletal tissues in 

 their neighbourhood. 



Our knowledge of the physiology of the "auditory" organ in the 

 lower Vertebrates is so imperfect that it is difficult to select a stand- 

 point from which to view the structural modifications it undergoes in 

 passing from the piscine to the amphibian type. Although we may 

 conjecture that in the fishes there is a perception of vibrations which 

 are transmitted from the surrounding medium, through the tissues of 

 the head or the wall of the capsule to the sensory areas of the laby- 

 rinth, yet it is only when we come to the Amphibia that definite 

 structural relations are found which leave us in no doubt as to their 

 significance.!) Within the limits of the latter group, the accessory 

 arrangements for the transmission of vibrations from the exterior to 

 the labyrinth range from a primitive to a comparatively efficient con- 

 dition. In the Urodela the only obvious structural advances on the 

 piscine type, are the formation of definite and constant perilymphatic 

 spaces and of the foramina and tympanal areas with which they are 

 associated. These modifications require explanation, and we want to 

 know, if possible, how the spaces first originated, and how they become 

 associated with the foramina. The latter is the more important question, 



^) See however, Howes [15], and Sagemehl [16]. 



