410 Mr. R. Broom on the 



logical value of the malleus and incus. The researches of 

 Peters '^j Dollo fj Baur |, and Gadow § place it beyond doubt 

 that the Mammalian auditory ossicles are together homolo- 

 gous with the Reptilian columella auris and extra-columella, 

 and that the malleus and incus can never have taken any part 

 in the articulation of the jaw. 



An entirely different view of the fate of the quadrate has 

 recently been revived by Albrecht ||, and has been supported 

 by Dollo, CopeH, and Baur. According to this view the 

 quadrate is represented by the zygomatic portion of the 

 squamosal. It is highly probable that the Mammalian 

 squamosal represents more than one element ; but the palaion- 

 tological evidence which would find in it the quadrate is 

 unsatisfactory, the zygomatic portion being most probably 

 homologous with the quadrato-jugal. 



Gadow and Seeley ** advocate the view of Cuvier and 

 Owen, that the quadrate is represented by the tympanic bone. 

 This, however, involves a gradual shifting back of the quad- 

 rate from the articulation, which, though conceivable, is not 

 borne out by positive evidence either from palaeontology, 

 embryology, or comparative anatomy. 



The Mammalia and Reptilia seem to have had a common 

 origin in a group of highly developed Amphibians, of which 

 no remains have as yet come to light, but of which Pareia- 

 sauriis is the nearest ally as yet known. In these ancestral 

 forms there was in all probability but a feebly developed 

 flattened quadrate, probably ossified and articulating with the 

 quadrato-jugal, squamosal, and pterygoid. In Pareiasaurus 

 Seeleytt says the quadrate bone "would appear to have been 



* W. Peters, " Ueb'^r die Gehorknoclielchen und ihre VerhJiltniss zu 

 den ersten Zungenbogen bei Spheiwdon jmnctatus,^' Monatsber. d. k. 

 preuss. Akad. d. Wiss., Berlin, 1874. 



t L. Dollo, " On the Malleus of the Lacertilia, &c.," Quart. Jouru. 

 Micr. Sc. 1883. 



X G. Baur, " On the Quadrate in the Mammalia," Quart. Journ. Micr. 

 Sc. 1887. 



§ H. Gadow, "On the Modifications of the First and Second Visceral 

 Arches, &c.," Phil. Trans, vol. clxxix , 1888. 



II P. Albrecht, ' Sur la valeur morphologique de I'articulation mandi- 

 bulaire, &c.,' Bruxelks, 1883. 



51 E. D. Cope, " The Relations between the Theromorphous Reptiles 

 and the Monotreme Mammalia," Prcc. Amer. Assoc. Adv. Sci. vol. xxxiii. 

 1884. 



** H. G. Seeley, " On the Anomodont Reptilia and their AUies," Phil. 

 Trans, vol. clxxx.,* 1889. 



tt H. G. Seeley, " On Pareiasav? us homhidens (Owen), and the Signifi- 

 cance of its Affinities to Amphibifins, Reptiles, and Mammals,'' Phil. 

 Trans, vol. clxxix., 1888. 



