1910.] The Origin of Mammals. 113 



and change of function, and (3) a constant search for the little-noticed, 

 palseotelic characters which are likely to prove the most significant of remote 

 relationship. 



CHAPTER I. THE ORIGIN OF MAMMALS AND THE PROBLEM 

 OF THE OSSICULA AUDITUS. 



Analysis. 



Page 



I. The Synapsid Reptiles 113 



The Diadectids, Chelonia etc 114 



Procolophon and the Pelycosaurs hot Synapsida 115 



Pareiasauria 115 



Dromasauria 116 



Therocephaha 116 



Anomodontia proper 117 



II. Relations of the Mammalia to the Triassic Cynodontia 117 



Primitive reptilian characters of the Cynodontia 118 



Characters in which the Cynodontia foreshadow the Mammalia . 118 



III. Evidence from comparative anatomy and ontogeny on the origin of the 



middle and outer ear 125 



The cartilages of the external ear 125 



The tympanic cavity 125 



The tympanic membrane 127 



The tympanic aniuilus ... 128 



The stapes 130 



The mammalian incus and l)ody of the malleus 130 



The anterior process of the malleus 132 



The manubrium of the malleus 132 



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



fate of the cjuadrate and articular 133 



Mechanical objection to the theoiy that the incus and malleus 



represent transformed jaw elements 135 



IV. Application to the conditions in the Cynodontia of the theory that the 



incus is derived from the quadrate, the malleus from the articular 136 



V. Summary 141 



The living and fossil Amphibia are admitted bv most contemporary 

 authorities to be very far removed in the sum of their characters from the 

 direct ancestors of the mammals. After a very careful review of the subject 

 Professor Kingsley (1900, pp. 250-255) concludes "that it is impossible that 

 the mammals have descended from any form distinctly urodelan nor is 

 there any known stegocephalan which will meet the requirements of the 



