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. In the 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 "pieces cutanees," 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'esten effet," he says, " cet os a la face interne duquel 

 l'os hyoide des poissons est suspendu, qui s'articule en haut avec le masto'i- 

 dien et tres souvent meme sur l'ecaille du temporal." So far as my obser- 

 vation has gone, it is a rare exception to find the hyoid arch suspended to 

 the preoperculurn ; the rule in osseous fishes is to find the upper styliform 

 piece of the hyoid arch (fig. 5, 3s) attached to the epi-tympanic (2s a) close 

 to its junction with the meso-tympanic bone (2s 6). 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 (' ecaille 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 (28 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 preoperculurn 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 preoperculurn, 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. Muller 

 attache, a ce qu'il parait, trop peu d'importance a ce fait, que toujours le 

 preopercule, et cela aussi chez les Siluroides, sert de point d'attache a l'arc 

 hyoiidien," 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 



* Annates des Sciences, 1845, p. 56. 



