236 report— 1846. 



hsemal or visceral cartilage of the mandibular arch in mammals, the homo- 

 logy of the malleus is so clearly traceable down to its first independent ma- 

 nifestation in coexistence with the tympanic membrane of the batrachia, to 

 which it connects the unequivocally acoustic ossicle representing the ' stapes,' 

 that the reference of all the additional ossicular mechanism of the ear-drum 

 to the same system of the skeleton as the petrosal itself, appears to me to be 

 most consonant with the recognised facts in their development and compara- 

 tive anatomy. 



M. Agassiz has never countenanced the idea of the reproduction of the 

 mammalian tympanic ossicles in a magnified form in either the tympanic 

 arch or its opei'cular appendages. Returning 1o the consideration of these 

 bones in the last volume (p. 68) of his admirable ' Recherches,' he reaffirms 

 his opinion, that the opercular, subopercular, and interopercular are *■ osse- 

 lets particuliers de la peau ;' but calls them ' branchiostegal rays.' If he 

 had meant that they were parts essentially distinct, but comparable to the 

 true branchiostegals, he would have accurately enunciated their ' serial ho- 

 mology.' M. Agassiz, however, expressly repudiates this idea of represen- 

 tative relation, and affirms them to be part of one and the same series of 

 rays. " Mais en disant que les pieces operculaires sont des rayons branchio- 

 stegues, je n'entends point faire une simple comparaison, mais bien affirmer, 

 que je considere ces plaques osseuses simplement comme les rayons bran- 

 chiostegues superieurs*." This idea is, in fact, a necessary consequence of 

 M. Vogt's conclusion, that the preoperculum is the upper or styloid element 

 of the hyoidean arch. The combination of the opercular rays or bones with 

 the branchiostegals in the support and movements of the continuous gill- 

 cover and gill-membrane, does not prove them to be diverging appendages 

 of the same arch, any more than the similar combination of the rays of the 

 pectoral and ventral fins in the sucker of the Cycloplerus proves those rays 

 to be parts of the same arch. And I may repeat that, admitting the humerus 

 to be, as Bakker surmised, confluent in all fishes with the bone 52, fio-. 5 ; 

 and since in the plagiostomes, sturgeons and lophioids, the second segment of 

 the rudimental fore-limb is not liberated from the supporting arch ; so, like- 

 wise, the proximal member of the opercular limb may remain, or become in 

 some instances confluent with its sustaining arch, without that exceptional 

 state invalidating the determination deduced from its more constant and re- 

 gular character as the proximal element of the free appendage to that arch. 

 The third inverted arch of the skull is suspended in fishes by a slender 

 styliform bone, the 'stylohyal' (fig. 5, 3s), from the lower end of the epi- 

 tympanic (2s a) close to the joint of the styliform 'mesotympanic' (23 b) ; 

 and it is connected, through the medium of the posterior division and 

 joint of the epitympanic, with the mastoid (s). Now, either that division 

 of the epitympanic may be viewed, by virtue of its proper articular condyle 

 above, and its connection with a distinct inverted arch below, as the proximal 

 piece of that arch, coalesced with the proximal piece of the next arch in 

 advance, which articulates with the post-frontal ; or, it may be viewed as an 

 excessive development of the proximal piece of the tympano-mandibular arch, 

 which, extending backwards, has displaced the hyoid from the mastoid, just 

 as the squamosal, by a similar backward development, in mammals, displaces 

 the mandibular arch from the tympanic. 



According to the first view, the bone no. 38 would be a dismemberment 

 of the proximal element of the hyoid arch ; according to the second view, it 

 would be the entire element reduced and displaced : in both cases it would 

 be homologous with the proximal slender piece of the hyoid arch in all 



* Recherches sur les Poissous Fossiles, v. pt. ii. p. 68. 



