ON THE VERTEBRATE SKELETON. 2.35 



or disturbing the connections of the true stylo-hyal (fig. 5, ss) with the epi- 

 tympanic (28a) from which it is normally suspended. 



M. Vogt correctly observes that the 'temporal' (epitympanic, 2s a), 'sym- 

 plectique' (mesotympanic, 2s b), and ' jugulaire' (hypotympanic, 2s d), "a 

 eux seuls forment deja un arc suspensoir complet, a la face posterieure 

 duquel le preopercule est seulement accole*." But this only proves that the 

 preoperculum is an appendage to such arch, not that it is a suspensory pier 

 of a second arch. 



The only essential modification which the siluroids present is the confluence 

 of the preoperculum with the true tympanic pedicle, here reduced to a single 

 piece. But this does not disprove its character as an appendage of the 

 tympano-mandibular arch, any more than does the confluence of the ulna and 

 radius with the scapular arch in the sturgeon disprove the character of those 

 elements as appendages of that arch. 1 have not been able to trace in the 

 siluroids the primitive boundaries of the coalesced preoperculum to such an 

 extent as to justify the statement, that it is intercalated between the epitym- 

 panic and hypotympanic, replacing the mesotympanic : but, if the preopercular 

 should extend in any siluroid fish so far as M. Vogt describes, this excep- 

 tional development would rather prove it to belong essentially to the tym- 

 panic and not to the hyoidean arch : at least it is only through this abnor- 

 mal encroachment that the preopercular can detach the stylohyal from the 

 epitympanic. 



As the otosteals, or ' ossicula auditus,' have borne a prominent share in the 

 discussions of the special homologies of the tympanic pedicle and its append- 

 ages, I may here remark that the extension in the embryo mammal of the 

 long and slender process of the malleus in the direction of the mandible, and 

 its continuation or connection with the cylindrical cartilage (haemal portion 

 of the tympano-mandibular arch) from which the lower jaw is subsequently 

 developed, is a circumstance which renders the idea of the malleus, at least, 

 being a modified element of the tympano-mandibular arch in batrachians 

 and fishes, worthy of consideration. The prolongation from the mesotym- 

 panic of the cylindrical cartilage, described by Meckel, and around which 

 the mandible is ossified in fishes, and the characteristic cylindrical or styloid 

 form of the mesotympanic, have induced M. Vogt-|- to view that bone, the 

 'symplectique' of Cuvier, as the homologue of at least part of the malleus; 

 and at the same time of the bone called ' tympano-malleal' by Duges (my 

 'hypotympanic') in the batrachians. M. Vogt offers no other reasons for 

 the determination. I find that the cartilage which in the batrachians forms 

 the medium of communication between the semi-ellipsoid ossicle (stapes) 

 closing the fenestra ovalis and the tympanic membrane, is repeated or repro- 

 duced in the more malleiform cartilage connecting the columelliform stapes 

 of the saurian reptiles to the membrana tympani. In birds a portion of the 

 cartilage attached to the tympanum becomes ossified and coalesces with the 

 columelliform stapes ; and at the angle of union one or two cartilaginous 

 processes exist, which some anatomists have compared with the incus. But 

 all anatomists have concurred in recognising the homology of the peripheral 

 bent-down portion of the long columella, which adheres to the membrana 

 tympani, with the part of the malleus called ' manubrium,' or handle, in 

 mammalia. The superadded modifications characteristic of the otosteals in 

 this class, have their seat between the manubrium mallei and the stapes, and 

 chiefly result in the development of the new bone called 'incus' and its epi- 

 physis, which has been termed the ' os orbiculare.' Notwithstanding, there- 

 fore, the connection of the 'processus gracilis mallei' with the embryonic 

 * Annales des Sciences, 1845, p. 55. f Loc. cit. p. 58. 



b 2 



