403 



Another question concerns the os tympanicum. With Peters I 

 look upon it as the homologue of the quadrate since it fulfills every 

 condition necessary for this comparison. To wit: it can be shown 

 that the tympanic of the Mammalia must have articulated by its dorsal 

 end with the squamosal region of the skull, by its ventral end with 

 the mandible, and that it sends out from the posterior side of the 

 middle of its shaft a process which curves backwards and upwards 

 and forms the greater part of the tympanic ring. The usual, now 

 time-honoured objection to this view is the statement that the tym- 

 panic of Man is a membrane bone and therefore cannot be homologized 

 with the quadrate which is part of the cartilaginous arch. Various 

 statements by Parker, Flower and others, to the eifect that a carti- 

 laginous base has been observed in the tympanic of several Mammals, 

 are brushed aside as doubtful. But supposing there were no cartilage 

 in it. Would that be the only instance of a bone developing now „in 

 membrane" only which has lost its cartilage? What about the palatine 

 and pterygoid bones of Birds and Mammals? They likewise appear 

 almost entirely as membrane bones, but is therefore the pterygoid of 

 Mammals no longer homologous with that of Reptiles? If not, then 

 it is time indeed to cease believing implicitly in the guiding value 

 of cartilage versus membrane bones. 



However, there is no need for anxiety. The annulus tympanicus 

 is not the same as the quadrate, but it is part of it, and Gegenbaur 

 has accepted Parker's suggestion that the annulus is derived from 

 the spiracular cartilage, which may chondrify with the otic process of 

 the quadrate pedicle. I have discussed this in op. cit. p. 477. Re- 

 cently ViLLY and Gaupp have come to my rescue against their will. 

 The latter says, op. cit. p. 1056 that the Anlage of the annulus in 

 Anura proceeds as a proliferation of cells at the outer, anterior corner 

 of the so-called proc. muscularis quadrati, which at this time is situated 

 below the eye. This mass of cells soon separates from the quadrate 

 and is considerably augmented, so that it soon surrounds the whole 

 blind end of the tube. This is all I want. The derivation of the an- 

 nulus from the quadrate is proved; it also accounts for the partly 

 cartilaginous development of the tympanic membrane. The bulk of 

 the ring, the tympanic bulla proper (not its alisphenoid analogon), 

 and the eventually long bony meatus develop now, in the higher 

 Mammalia, without going through a cartilaginous stage, something 

 hke the pterygoids of Birds. 



Gegenbaur suggests that the os tympanicum (or at least so far 

 as it behaves like a membrane bone, or Deckknochen to the carti- 



26* 



