36 SKELETON OF THE FJSII. 



brain and organs of sense, but likemse the heart and 

 breathing organs. The inferior or "h^mal" arches are 

 greatly developed accordingly, and their diverging append- 

 ages support membranes that can act upon the surround- 

 ing fluid, and are more or less employed in locomotion; 

 one pair of these appendages, P, 57, answers, in fact, to the 

 fore-limbs in higher animals, and their sustaining arch, 

 51, 52, in many fishes, also supports the homologues of 

 the hind-limbs, V, 69. Thus brain and sense-organs, jaws 

 and tongue, heart and gills, arms and legs, may all belong 

 to the head ; and the disproportionate size of the skull, and 

 its firm attachment to the trunk, required by these func- 

 tions, are precisely the conditions most favorable for facili- 

 tating the course of the fish through its native element. 



It may well be conceived, then, that more bones enter 

 into the formation of the skull in fishes than in any other 

 animals; and the composition of this skull has been 

 rightly deemed the most difficult problem in comparative 

 anatomy. " It is truly remarkable," writes the gifted 

 Oken, to whom we owe the first clue to its solution, 

 " what it costs to solve any one problem in philosophical 

 anatomy. Without knowing the wliat., the hoiu^ and the 

 ichy^ one may stand, not for hours or days, but weeks, 

 before a fish's skull, and our contemplation will be little 

 more than a vacant stare at its complex stalactitic form." 



To show luhat the bones are that enter into the com- 

 position of the skull of the fish ; hoib\ or according to what 

 law, they are there arranged ; and luliy^ or to what end, 

 they are modified, so as to deviate from that law or arche- 

 type, will next be our aim. These points, rightly under- 

 stood, yield the key to the composition of the skull in all 

 vertebrata, and they cannot be omitted Avithout detriment 

 to the main end of the most elementary essay on the 



