206 



DR. B. PETRONIEVICS ON THE LOWER JAWS OF THE 



the question of the origin of the Ossicula auditus in Mammals. 

 Our specimen shows the beginning of the separation of the 

 articular bones from the dentary, a state of things that the 

 classical theory of the origin of Mammalian ossicula auditus 

 necessarily presupposes. As we have seen, the bony connexion 

 between the articular bones and the dentary is a relatively much 

 reduced one, especially in the hind part (comp. text-fig. 1). The fact 

 that the quadrate has been lost in our specimen on the left side, 

 where it might have been preserved, shows that it was probably 

 only insufficiently fixed in the corresponding groove of the 

 squamosal. The movable condition of the quadrate, that the 

 classical theory presupposes, is here, as it seems, also in its 

 beginning. And finally we find in our specimen on the left side 

 a displaced bone (comp. text-fig. 1, st.), that is, according to 

 another specimen, to be considered as the bone connecting the 

 region of the fenestra vestibuli with the quadrate, consequently 

 as the stapes or the columella' (on this bone comp. Seeley (1 

 1895, p. 25, Broom 1904, p. 491, who considers it in Cynognathus 

 platyceps wrongly as a tympanic ring, and especially Watson, 

 1911, p. 324). 



From the above it follows that we have in Gomphognathus 

 realized all the elements that constitute the morphologically 

 initial state in the evolution of the mammalian ossicula auditus, 

 and we have only to suppose that in the descendants of the cor- 

 responding relatives of Gomphognathus (the direct ancestors of 

 Mammals) this state of things increased in the direction of a 

 further separation of the stapes-quadrate -articular bone chain 

 from the squamosal and dentary bones, in order to reach the final 

 state, when in true Mammals the former were transformed into 

 the ossicula auditus. Into the question how this transformation 

 took place, and into the corresponding question of the homologies, 

 I cannot enter here (comp. the Literature, Nos. 7-11). I mention 

 only that the tympanic membrane of the Mammals is most pro- 

 bably a neomorph (and I agree in this point with Gaupp — comp. 

 Gaupp, 1911, p. 641 seq. and p. 659, while in many other con- 

 clusions readied by Gaupp — comp. p. 633 and p. 656 — I must 

 disagree), and that the manubrium mallei in Mammals cannot be 

 homologized with the extra-col umella of the Reptiles, as Kingsley 

 does (comp. Kingsley, 1900, p. 232 seq.). 



In finishing this paper I desire to express my tha.nks to 

 Dr. Smith Woodward and Dr. Andrews, of the British Museum 

 (Natural History), for the loan of the new preparations (executed 

 by Mr. Hall), and to Dr. Andrews for some valuable help. 



Literature. 



1. H. G. Seeley. — Researches on the Structure, Organization, 

 and Classification of the Fossil Reptilia. Part IX. Section 4. 

 On the Gomphodontia. In ' Philosophical Transactions 

 Royal Society,' 1895, vol. 186, B, pp. 1-58 (On GompKo- 

 (jnath us, pp. 3-31). 



