No. 2304. REPTILIAN CHARACTERS IN 2IAMMALS—W0R.TMAN. 37 



In a like manner the bone which I have described as the paramas- 

 toid may represent the vestige of that part of the quadrate which 

 was formerly attached in this identical position. 



In accordance v/ith this conception that tlie vestigial element under 

 discussion represents only a portion of the inner part of the original 

 quadrate, we can readily understand its relations to the tympanic 

 ring and v/hy this latter bone should lie upon the outside of it. It 

 will be recalled that the tj^mpanic membrane or the eardrum is 

 attached in the reptile largely to the outer edge of the quadrate, and 

 when this bone began to disappear a new mem.brane bone v/as 

 developed in the outer circumference or periphery of the membrane, 

 namely, the tympanic ring — in order to afford the proper support 

 for the drum. This is actualhv^ the case in some birds, notably the 

 peafowl and others. Developing as it did in the periphery of tlie 

 membrane, it would be manifestly impossible for it to be formed on 

 the opposite side or inside of the quadrate, since its special ofhce was 

 the support of the eardrum, and hence as the quadrate was reduced 

 to a vestige we find it lying upon the inner side of the tympanic. 

 This fact supplies a powerful and convincing argument in favor of 

 this interpretation of its homology with this part of the reptilian or 

 batrachian quadrate. In fact I can not conceive of any other inter- 

 pretation that can be placed upon it. It will thus be seen that the 

 fate of the reptilian quadrate in the skull of the mammal was not, as 

 supposed by Gadow, to become the t^nrnpanic, nor its transformation 

 into the fibro-articular cartilage of the glenoid cavity as surmised by 

 Broom, nor its absorption into the squamosal as held by Cope and 

 Baur; but in a large number of mammals it still persists developed 

 in the premallear tract of Meckel's cartilage, and either attached to 

 the processus gracilis or incorporated with the tympanic or botli. 



In regard to the value of the evidence derived from the skull of 

 Ornithorhynchus, already mentioned, I am not in a position at tlie 

 present time, through lack of suitable material, to say whether or 

 not the bone above described represents a distinct ossification and 

 arises as a separate element from Meckel's cartilage in the embryo, 

 but should such prove to be the case it will then offer pov^^erfiil 

 confirmator}^ evidence of the mterpretation herein considered. It 

 ma,Y be stated, however, that Watson * in a late paper on the 

 Monotreme skull makes no mention of such an element, but whether 

 his material was of a suitable stage to show it if present I have no 

 means of knowing. 



One of the insuperable objections that was urged by Gadow 

 against this transposition theor}^, to the effect that it is inconceivable 

 how the change could have taken place without seriously impairing, 



I Trans. Philos. Soc, Ser. B, vol. 207, 1916, pp. 311-374, pis. 23-25. Not received in time for use in 

 thi? connection. 



