1910.] Fate of the Quadrate; Gaupp's Diagram. 135 



mal lies in front of the articular and is a part of Meckel's cartilage, and there- 

 fore belongs to the first gill arch. The cogency of Gadow's argument on 

 this point seems therefore to be open to doubt. 



The Fate of the Quadrate. — Various other theories have been proposed 

 to account for the fate of the quadrate in the mammalia. 



Albrecht (1884) held that the quadrate became reduced and was absorbed 

 in the squamosal; but the principal evidence he adduced in support of this 

 view was a malformed idiot's skull which showed on one side a separate 

 bone in the assumed position of the cjuadrate. This is a fair example of the 

 kind of "evidence" which formerly was often accepted in the domain of 

 comparative anatomy and even of paleontology. Isolated points of re- 

 semblance between the most widely removed forms were used to support 

 far reaching homologies, with little regard to the totality of evidence drawn 

 from all parts of the organism. 



Osborn also (1898, p. 331), in view of the great reduction of the quad- 

 rate in the Cynodonts, not unnaturally favored the theory that the quadrate 

 had been absorbed into the squamosal, but this view (which was also held 

 by Baur) lacks direct confirmatory evidence. 



Broom (1890, 1906, 1907.3) sees in the reduced quadrate of the Cyno- 

 donts the homologue of the interarticular disc, or meniscus, which lies be- 

 tween the mandibular condyle and the glenoid fossa of mammals {cf. Fig. 

 5, C). The presence of an ossified meniscus in the rodent Pedetes proves 

 only that this element may occasionally become ossified. Further consider- 

 ations on the origin of the meniscus are given below (p. 138). 



Supposed mechanical objection to the theory that the incus and malleus 

 represent transformed, jaw elements. 



From the foregoing it appears possible but not by any means proven 

 that the middle elements of the mammalian ossicular chain have attained 

 their present relations through a change of function, whereby they gradually 

 become relieved of the jaw-supporting function and, being pushed against 

 the stapes-extracolumella, came thus to participate in its function of trans- 

 mitting vibrations to the inner ear. Gaupp (1905, p. 136) has undertaken 

 to conceive the conditions during the time when the new and old joints both 

 functioned together; but in his diagram, which is based on the conditions 

 in the Lacertilia, the anterior joint, between the new mandibular condyle 

 and the squamosal, is separated by a considerable interval from the old 

 joint, between the articular and the quadrate. 



Apart altogether, however, from the fact that all known streptostylic 

 reptiles belong to the Diapsida, which appear to be widely removed in many 



