230 report— 1846. 



of the squamosal, than the proximal or uppermost piece (23a) to which Cu- 

 vier has applied that name. Tf, indeed, Bojanus could have determined to 

 his own satisfaction or that of other anatomists, that the pedicle (28, fig. 23), 

 articulated by one end to the mastoid, and by the other to the mandible, in 

 birds, was the 'squamosum,' then there would have been some ground for 

 regarding the bone (28a, fig. 5) connected in fishes, with the mastoid as the 

 ' squamosum.' 



But when Cuvier had persuaded himself that the bone no. s, fig. 23, in 

 birds, to which the tympanic pedicle is articulated, was the ' ecaille du tem- 

 poral,' we feel at a loss to know on what principles special homologies can 

 be traced, when we find the name transferred to the upper part of the tym- 

 panic pedicle in fishes (fig. 5 28 a), which is articulated to the bone (s) un- 

 equivocally answering to Cuvier's ' ecaille du temporal' in birds. M. Agassiz 

 is more consistent, and abandons with reason the Cuvierian determination of 

 the squamosal in fishes : if, however, the grounds assigned are conclusive as 

 to the homology of no. s, figs. 8 & 23 in birds with the mastoid of mammals 

 and reptiles, M. Agassiz cannot be correct in regarding the bone no. 8, fig. 

 5 in the fish, as the ' ecaille du temporal.' 



With reference to the idea entertained by Spix, Geoflroy and Agassiz, of 

 the homology of the suborbital muciferous scale- bones in fishes with the malar 

 bones of higher vertebrates, I may refer to what has already been said in 

 regard to the actual repetition of the osseous arch connecting the prefrontal 

 with the postfrontal in certain birds, where that arch coexists with, and in- 

 dependently of, the bone recognised as the 'malar' by both Spix and Geof- 

 froy. The connection of the malar with the lacrymal and post-frontal is 

 less constant and characteristic of the bone than that with the maxillary and 

 squamosal. And it may further be remarked, that the functional character 

 of circumscribing a mucous duct, manifested by the lacrymal or anterior 

 end of the upper zygomatic or suborbital arch in the parrot, is superadded to 

 the character of connections in proof that such arch, and not the true zygo- 

 matic arch below, is homologous with the suborbital chain of bones in fishes. 

 All these discrepancies as to the jugal and squamosal in fishes arise, in my 

 opinion, out of the circumstance that those bones are normally absent in 

 that class; both 26 and 27, figs. 11, 22, 23, 24, 25, being accessory parts, de- 

 veloped only in saurians, chelonians, birds and mammals, for additional fixa- 

 tion of the upper jaw, or for additional expansion of the cranium, or for both 

 purposes*. 



According to this view, I regard the tympanic (2s) as essentially charac- 

 terized in the oviparous vertebrates (fishes, reptiles, birds) by its free articu- 

 lation by a convex condyle with the mastoid above, and by a convex condyle 

 with the mandible below ; and I regard its subdivisions in the lowest of 

 these vertebrates, in the same light as the subdivisions of the mandible itself. 

 The formation of the tympanic cavity and support of the tympanic membrane 

 are secondary functions. The tympanic pedicle is essentially a single cranial 

 element, and actually so in all air-breathing vertebrates above batrachians. 

 We see plainly, even in the frog, that the portion which supports the 'mem- 

 brana tympani' is a mere exogenous process of the pedicle : it has still less the 

 appearance of a distinct part or process in the saurians, chelonians and birds : 

 and when the tympanic is excluded by the squamosal in mammals from its 

 normal office of supporting the mandible, it still manifests its character of 



* The inconstant ossicle suspended to the back part of the free extremity of the maxillary 

 in the percoid fishes would have the best claim to homology with the malar, if the further 

 subdivision of the maxillary in the herring and lepidosteus did not indicate it to be a vege- 

 tative dismemberment of that bone. 



