1910.] Origin of the Incus and Malleus; Fate of the Quadrate, etc. 133 



If the manul)riiini has not had a phylogcnetic history distuict from that 

 of the body of the malleus this would constitute an objection to homologizing 

 the malleus with the articular (see below). 



Rival hypotheses of the origin of the incus and malleus and of the fate of the 



quadrate and articular. 



Gadow (1901, pp. 396-398) believes that both the incus and the malleus 

 have been derived from the reptilian columella and its appendages, the 

 suprastapedial, etc. This opinion is also held by Broom (1907.3, pp. 10-11"), 

 while similar views were held by Peters, Dollo, Baur and Cope (1883). These 

 all base their argument chiefly on the similarity in function and relations 

 between the extracolumella and the incus and malleus; because, as stated 

 above, the extracolumella, like the manubrium of the malleus is fastened ex- 

 ternally in the tympanic membrane, while internally, like the incus, it articu- 

 lates with the stapes. Kingsley held that the malleus is really a compound 

 bone and that the assumed homology with the extracolumella applies only to 

 the manubrium, but as stated above Kingsley's view that the manubrium is a 

 separate element has not been confirmed. The extracolumella of the Croco- 

 dile has a dorsal process called the suprastapedial, which Broom (1907.3, p. 

 10) homologizes with the incus. On the other hand the variability of the 

 extracolumellar processes of the Reptilia and the difficulty of homologizing 

 them within the class (Gadow, 1901, j>. 399) rather warns against attempt- 

 ing to seek the homology of one of them in the mammals, which lie so far 

 outside the limits of the modern Diapsida. If Broom and Gadow are right 

 then the Crocodile is more primitive than Sphenodon with respect to its 

 auditory ossicles. Broom's hypothetical diagram (1907.3, p. 10, cf. Fig. 5 

 above) of the ossicula in an embryo Cynodont is in fact a graphic average 

 between the embryonic conditions in the Crocodile and in the mammal. 



Another comparison in favor of homologizing the incus and malleus with 

 the extracolumella and its appendage the suprastapedial respectively, has 

 been adduced by Gadow (1901, p. 398). In the embryo crocodile (cf. Fig. 

 5, A, col. art) the extracolumella is joined with the posterior or articular 

 ex])ansion of Meckel's cartilage by a bar of cartilage or connective tissue, 

 which may be designated as the "columella-articular" bar. In the embryo 

 mammal (Fig. 7, C) the malleus is prolonged anteriorly into the ]\Ieckelian 

 cartilage, and the part in front of the malleus may be designated as the 

 "malleo-meckelian" bar. Since the extracolumella has the same relations 

 to the "columella-articular" that the malleus has to the "Malleo-meckelian" 

 Gadow homologizes the extracolumella with the malleus (the incus is as- 

 sumed to be a part of the same mass). But this argument simply begs the 



