ON THE VERTEBRATE SKELETON. 325 



M. Vogt. With regard to the series of nine arches into which the facial 

 bones are distributed, it may be remarked that the independence of the maxil- 

 lary from the palatine, which is more apparent than real in the osseous fishes, 

 ceases to be manifested in any degree in the plagiostomes and lepidosiren : 

 that the first and second arches are suspended by their crowns with their 

 haunches projecting freely outwards, whilst the third and fourth arches are 

 suspended, in the reverse position, viz. inverted, with the crowns or key-stones 

 downwards : the four next arches are rather complete cinctures, their sum- 

 mits meeting and being loosely suspended to the basis cranii, or, in pla- 

 giostomes and cyclostomes, to the under part of the vertebral column of the 

 trunk. Although professing to base his classification upon developmental 

 characters, M. Agassiz owns with regard to the posterior branches of the 

 maxillary arch, e. g. the suborbitals, " that they appear to be rather formed 

 by the dermal system." And this is unquestionably true : whilst the pala- 

 tines, which are the true piers of the arch, are developed from the blastema 

 of the same visceral arch as the maxillaries and premaxillaries. 



The error in regard to the special homology of the suborbital bones, deter- 

 mined by M. Agassiz as the malars, and which is so clearly exposed by the 

 structure of the skull of the Psittacidce (ante, p. 209), has misled him in re- 

 spect to the natural and typical constitution of the maxillary arch. 



The mistake in reference to the special homology of the epitympanic (28a), 

 determined by M. Agassiz as the ' mastoid,' has, in like manner, influenced 

 him in dissociating it from the other dismemberments of the tympanic pedicle, 

 and referring it to a different arch. 



With regard to the hyoid and branchial arches, it will be observed that 

 M. Agassiz makes no distinction between the systems of the neuro- and 

 splanchno-skeleton. An arch constant and ossified in all vertebrates where 

 the rest of the endoskeleton is ossified, and which, even admitting M. Agassiz' 

 special homology of the preopercular as the styloid process of the temporal, 

 would still be suspended in the inverted position, like a true haemal arch, is 

 placed in the same category as the branchial girdles, which are often cartila- 

 ginous when the hyoid is osseous, in bony fishes ; and which disappear, in the 

 metamorphosis of the tadpole, with the evanescent respiratory viscera for 

 the support of which they are exclusively developed. 



The constitution of a distinct 9th facial arch for the posterior pair of bran- 

 chial girdles, which retain their gills in lepidosiren, though modified in sub- 

 servience to mastication in most osseous fishes, appears to be giving undue 

 importance to an artificial or adaptive character. Finally, the natural con- 

 nections of the scapulo-coracoid arch in osseous fishes are totally disregarded, 

 and it is left out of the enumeration of the bones of the head. 



The unbiassed anatomist may find an element forjudging of the natural 

 character of the cranio-vertebral system propounded in the present Report, 

 by contrasting the classification of the bones of the fish's skull to which it 

 leads, with that proposed by M. Agassiz, and with nature*. 



Having thus responded to the objections advanced by Cuvier and M. 

 Agassiz to the interpretations of the segmental constitution of the bones of 

 the head which were open to the criticism of those great authorities in 

 anatomy, I proceed briefly to explain the segmental constitution of the bones 



* I am bound here to say that in the discussion of the subject of this Report with M. 

 Agassiz, which, amongst other advantages of the meetings of the British Association, I en- 

 joyed at Southampton, he admitted, with his characteristic frankness, that somepoints of 

 his classification of the bones of the head in fishes would require reconsideration. One of 

 the eminent physiologists who was present at the debate which followed the reading of the 

 Report, has recorded the impression it produced upon him in a review of my ' Hunterian 

 Lectures on Vertebrata ' in ' The British and Foreign Medical Review,' No. xlvi. p. 490. 



