324 REPORT—1846. 
arch, and correspond, in serial homology, with the branchiostegal appendages 
of the hyoid and the pectoral appendages of the scapular arches, and have 
the same title to be regarded as cephalic fins, and as parts of the normal 
system of the vertebrate endo-skeleton; but neither opercular bones nor 
branchiostegal rays are retained in the skeletons of higher vertebrata. All 
diverging appendages of vertebral segments make their first appearance in 
the vertebrate series as ‘rays’; and the opercular bones are actually repre- 
sented by cartilaginous rays, retaining their primitive form in the plagio- 
stomes. Inthe conger the subopercular still presents the form of a long and 
slender fin-ray. 
The opercular and subopercular, in ordinary osseous fishes, may frequently 
coalesce, like the suprascapular, with their representative scales of the dermal 
system ; but they are essentially something more than peculiarly developed 
representatives of those scales. M. Agassiz, indeed, excepts the preoper- 
cular bone from the category of “piéces cutanées,” believing it to be the 
homologue of the styloid process of the temporal bone in anthropotomy, or 
the ‘stylo-hyal’ of vertebrate anatomy, as the piece, viz. which completes the 
hyoid arch above. “C'est en effet,” he says, “cet os ala face interne duquel 
los hyoide des poissons est suspendu, qui s‘articule en haut avec le mastoi- 
dien et trés souvent méme sur l’écaille du temporal.” So far as my obser- 
vation has gone, it is a rare exception to find the hyoid arch suspended to 
the preoperculum ; the rule in osseous fishes is to find the upper styliform 
piece of the hyoid arch (fig. 5, 3s) attached to the epi-tympanic (28 a) close 
to its junction with the meso-tympanic bone (28). It is equally the rule to 
find the preopercular (34) articulated with the epi-, meso-, and hypo-tym- 
panics ; and it is an exception, when it rises so high as to be connected with 
the mastoid (‘écaille du temporal’ of Agassiz). If the stylo-hyal be not the 
upper piece of the hyoid arch displaced, and if the upper piece connecting 
that arch with the mastoid is to be sought for in osseous fishes, I should 
rather view it in the posterior half of the epi-tympanic (2s a), which is usually 
bifurcate below and very commonly also above, when the posterior upper 
division articulates with the mastoid, and one of the lower divisions with the 
hyoid arch. 
The normal position, form, and connections of the preoperculum clearly 
bespeak it to be the first or proximal segment of the radiated appendage of 
the tympano-mandibular arch: the opercular, subopercular, and interoper- 
cular bones form the distal segment of the same appendage. 
M. Vogt, in supporting M. Agassiz’s views of the Ganoid order, reiterates 
his original idea that the preopercular bone is the proximal piece (styloid) 
of an arch distinct from the tympano-mandibular one ; but as the chief ground 
of this opinion rests on a simple question of fact easily determinable, viz. 
whether, as a rule, the hyoid arch is suspended from the preoperculum, and 
this from the mastoid in fishes, neither of which accord with my observation 
of their connections of those parts, the verdict may be left to the experience 
of other observers. From a remark of M, Vogt’s*, viz. that “ M. Miller 
attache, 4 ce qu'il parait, trop peu d'importance a ce fait, que toujours le 
préopercule, et cela aussi chez les Siluroides, sert de point d’attache a l’are 
hyoidien,” it would seem that, perhaps, the accomplished physiologist and 
ichthyologist of Berlin had not found the fact ; and, therefore, gave not more 
than its due importance to the rare exceptional circumstance of such an at- 
tachment. The preopercular can be removed in most fishes, except where, 
as in the siluroids, it coalesces with the tympanic arch, without dislocating 
* Annales des Sciences, 1845, p. 56. 
