132 Bulletin American Museum of Natural History, [^^ol. XXVII, 



squamosal. Moreover, as shown by Kingsley (cf. 1900, figs. 10, 14) the 

 incus of mammals and the quadrate of rei)tiles both lie above and in front 

 of the chorda tympani, while the malleus of mammals and the articulare of 

 reptiles lie below and behind the chorda tympani (Fig. 4). Broom, however 

 (1907.3), does not think that these comj^arisons prove that the incus is 

 homologous with the malleus, and he believes that the position of the chorda 

 tympani in mammals is secondary (c/. p. 143). 



The tensor tympani muscle, which is inserted into the manubrium mallei 

 is thought to be a derivative of the pterygoid muscle because it is innervated 

 by the third or mandibular branch of the fifth nerve (Weber, 1904, pp. 

 144-145^ IGO). This favors the view that the malleus represents a lower 

 jaw element, the articular. 



The anterior process of the malleus. 



Below and around the cartilaginous bar (Figs. 2C, 45) which connects 

 the developing malleus with the Meckelian cartilage a dermal splint is 

 formed {cf. Parker's figures of embryonic mammals, 1886), which seems to 

 occupy the position of the angulare in Ci/nognathus (Fig. 2, No. 2) and which 

 Parker and other authors have homologized A\'ith the angulare of modern 

 reptiles. This derm bone is variously named the processus "longus," 

 "gracilis," "Folianus," "anterior." 



Tlie manubrium of the malleus. 



The manubrium mallei (Fig. 2B, 7C), being fastened in the middle layer 

 or membrana propria of the tymi)anic membrane (]). 127) corresponds with 

 the extracolumella of reptiles, which is also fastened between the inner and 

 the outer membrane {cf. p. 127). Kingsley (1900, p. 232) states that in the 

 pig the manubrium "arises distinct from the body of the malleus" and is at 

 first, like the extracolumella, "a sei)arate element developing in the tympanic 

 membrane and only later uniting with the rest of the structure." Mead 

 however (1909, p. 188, and pi. iii) found that the manubrium in the pig was 

 continuous with tli* malleus, Fischer (1901, ]). 501, and Taf. xxx. Fig. 4) 

 found the same condition in the mole and Dr. Broom informs the writer 

 that the same is true in the Marsupials, and that in his opinion the manu- 

 brium has not been derived independently of the maleus. Kingsley's figures 

 show that the extracolumella, like the manuljrium, arises below and exter- 

 nally to the tympanic cavity and much below the level of the stapes and quad- 

 rate or incus ; and that the extracolumella further agrees with the manubrium 

 in its position with reference to the chorda tympani and " hyomandibular " 

 nerves: namelv below the former and above the latter (Fig. 4, A). 



