236 REPORT— 1846. 
heemal 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 opercular appendages. Returning to 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 piéces operculaires sont des rayons branchio- 
stégues, je n’entends point faire une simple comparaison, mais bien affirmer, 
que je considére ces plaques osseuses simplement comme les rayons bran- 
chiostégues supérieurs *,” 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-membrare, 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 Cyclopterus 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 sg, fig. 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’ (2s 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 _ f 
as the squamosal, by a similar backward development, in mammals, displaces 
the mandibular arch from the tympanic. J 
According to the first view, the bone no. 3s 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 Poissons Fossiles, v. pt. ii. p. 68. 
