15)10.1 



AXl) lilOLOOV OF THE r.AKGKU c'i:tacea. 



5 inches long and 1^ inches broad at the wider end. It consisted 

 of a deposit of ear-wax, which formed a coat to the outer sui-face of 

 the tympanic membrane in that region where the latter projected 

 into the external auditory meatus. The deposit formed a solid 

 mass, which could easily be detached from the tympanic membrane. 

 The inner portion of the plug had the form of an oval cup 

 (PL LXXIV. fig. 2, a), measuring about 1^ inches acro.ss tlie 

 broadest part and approximately 1 inch deep. The outer portion, 

 however, formed a solid thin flattened rod about 4 inches louf 

 and 1 inch broad (PI. LXXIV. fig. 2, b). The auditory canal 

 appeared to be full of water, in which tlie tympanic membrane 

 was immersed, with the attached plug of wax lying in a horizontal 

 position. The total length of the membrane andplugthusprojectiii" 

 into the auditory canal was about 6 inches (PL LXXIV. fig. .-J). 



The Cetacea have a remarkable depression on tlie base of the 

 ciuniam on each side of the median line (text-fig. 71). 



Text-fig. 71. 



Ventral view of left posterior portion of the skull oi Balcennptera musrulns Linn;eu.s 

 The tympanic bone has been removed. 



J'a = Frontal ; Prt. = Palatine; T'rt. = Vomer ; .i/.=Alisplienoi(l ; P^ = Pterygoid ; 

 -Pf-^ = Pterygoid plate of alisphenoid ; Pi.-= Portion of pterygoid, forming- roof 

 of pterygoid fossa; .Sr/. = Zygomatic jn-ocess of squamosal; .S'7.' = Zygomatic 

 process of squamosal, forming roof of groove in which lies the inner jiortion of 

 the external auditory ineatus with the plug of ear-wax ; «, anterior i)edicle for 

 attachment of tympanic bone, situated on pro-otic ])ortion of periotic ; h, fenestra 

 ovalis, situated on the labyrinthic segment of periotic; c, posterior pedicle of 

 tympanic bone, situated on opisthotic portion of i)eriotic ; Op., opistliotic portion 

 of periotic ; Bo., basioccipital ; JE.ro., exoccipital. 



In Bcdcenoptera these depressions are bounded postei'iorlv by 

 the projecting edge of the exoccipital, externally by the base of the 

 zygomatic [)rocess of the squamosal, on the inner side behind by 



