THE SKULL OF OSSEOUS FISHES. 



87 



formation of the cranial cavity of man and most Mammals, lias no 

 share in its formation in the lower Vertebrata. 



The two classes of cranial and facial bones, having been originally 

 founded upon the exclusive study of the most peculiarly and ex- 

 tremely modified skull in the whole Vertebrate series — that of Man, 

 — their characters, as might be expected, are artificial, and applicable 

 to tlie same bones in only a small proportion of the Vertebrata ; the 

 unity of the plan pervading the organisation of which it is the business 

 of the Anatomist, properly so called, to demonstrate. 



The bones of the skull of Fishes are primarily divisible into 

 those of 



A. Neuro-skeleton ; 



B. Splanchno-skeleton ; 

 c. Dermo-skeleton. 



A. The bones of the neuro- or proper endo-skeleton are arranged 

 here, as in the rest of the body, in a series of horizontally succeeding 

 segments ; each segment consisting of an upper (neural) and a lower 

 (hosmal) arch, with a common centre, and with diverging appendages. 

 As the bones, respectively entering into the formation of these seg- 

 ments, are the same in relative position, and nearly the same in 

 number, as in the typical vertebree of the trunk — the excess arising 

 from subdivision of peripheral elements — the same term ought to be 

 extended to those cranial segments which has been usually restricted 



Disarticulated bones of the cranial vertebra- and sense-capsules, [the haemal arches (ii, h) and 

 appendages in diagrammatic outline,] Cod-lish, Giidus Morrhua. 



g4 



