28 WILLIAM K. GREGORY 
7. The streptostylic condition of the incus (quadrate) in mam- 
malian embryos was held (’10 b, p. 600) to be a caenogenetic result 
of its secondary function as an accessory auditory ossicle.? 
“In the brief time that has elapsed since this application of 
Reichert’s doctrine to the conditions observed in Cynodontia, 
considerable collateral evidence has become available and cer- 
tain doubtful questions appear to be nearer to solution. Gaupp’s 
remarkable studies on the lower jaw of vertebrates (see pp. 18- 
21) have practically demonstrated that the mandibular joint 
of mammals is a secondary joint connecting the squamosal and 
the dentary; hardly less rigorous is his proof that the malleus 
represents the gonio-articulare, the incus the quadrate, of rep- 
tiles. On the other hand, all of Broom’s recent work (11) has 
brought cumulative evidence for the view that the Cynodonts 
are phylogenetically very near to the ancestral mammals. 
First in importance among the points discussed but left in 
doubt in the writer’s earlier paper is the homology of the rod- 
like bone (fig. 18, stp.) in Cynodonts which Broom formerly 
identified with the mammalian tympanic. It has, however, every 
appearance of being the bone usually called stapes in Permian 
reptiles (e. g., Dimetrodon, Case, ’07, pl.-19, fig. 2; Labidosaurus, 
Williston, 710, pl. 2). It also has the appearance of being 
homologous with the true stapes of Sphenodon. Gaupp (11, 
p. 641) thinks it highly probable that the doubted element is 
a stapes and that, as in Dimetrodon, its outer end was in 
contact with the quadrate. 
Dr. Broom, in a letter to the writer dated July 20, 1911, stated 
that he had decisive evidence showing that the doubted element 
is stapes and not tympanic. In Broom’s figure (’11, p. 7, pl. 
46, fig. 8) of the very primitive Cynodont Bauria this supposed 
stapes runs out toward the quadrate; its distal end is imperfect, 
but Broom restores it in contact with the quadrate. The stapes 
is represented as reaching nearly or quite to the quadrate in 
Cynognathus (Broom, ’04, pp. 490-498, pl. 25) and Oudenodon 
(Broom), Dimetrodon (Case), Labidosaurus (Williston), as well 
7 In view of the radical change of function some caenogenetic conditions in 
modern ontogeny are, from all analogies, to be expected. 
