222 Professor Owen's Teleology of the Skeleton of Fishes. 



fishes into several partly overlapping pieces adds, to its strength, and 

 by permitting a slight elastic bending of the whole, diminishes the 

 liability to fracture. The enormous size, moreover, of the tympano- 

 mandibular arch, and of its diverging appendages, contributes to en- 

 sure that proportion of the head to the trunk which is best adapted 

 for the progressive motion of the fish through the water. But with- 

 out the admission and appreciation of these preordained adaptations 

 to special exigencies in the skeleton of fishes, the superior strength 

 and complex development of the tympanic pedicle, and its appendages, 

 would be inexplicable and unintelligible in this lowest and first-born 

 class of Vertebrate animals. 



In contrasting the skeletons of the Fish and Mammal, with re- 

 ference to hypothetical secondary origins of organic species ; such, 

 for example, as that of transmutation and progressive ascent of spe- 

 cific forms, the vast disparity of the hyoidean arch, in point of size, 

 complexity, and strength, both intrinsic, and as due to its connec- 

 tions, must not be overlooked. Its small size, simple structure, and 

 loose suspension in the flesh, have led to its being reckoned in An- 

 thropotomy as a single bone ; and it is rarely preserved in the arti- 

 ficial skeletons of man or beast; whilst, if absolute and relative 

 magnitude, complexity of structure, and importance of function, are 

 tests of the grade of organization of a part, the progress of develop- 

 ment must be held to have been reversed in respect of the hyoid 

 arch ; which, with its appendages, ofl^ers the highest grade in fish, 

 and the lowest in man. And why this great difference — this strik- 

 ing exception to the general condition of the ichthyic organization % 

 It is explicable only on teleological principles. It is true the Fish 

 tastes not with its tongue, neither does it speak ; the sole function of 

 the human tongue bone, which is performed by that of the fish, is 

 that which is in subserviency to deglutition. But this function is not 

 in relation to food alone ; all the mechanical part of breathing in the 

 fish is a modified act of swallowing. The hyoid arch is the chief 

 point of suspension of the visceral arches which support the gills ; 

 and the branchiostegal membranes, stretched out upon the diverging 

 rays of the hyoid arch, regulate the course and exit of the respira- 

 tory currents ; thus the mechanical functions of the thorax of the 

 air-breathing classes are transferred to the hyoid arch and its ap- 

 pendages in fishes. 



By the retraction of the hyoid arch, the opercular doors are forced 

 open, and the branchial cavity is widened ; whilst all entry from 

 behind is prevented by the branchiostegal membranes, which close 

 the posterior branchial slits ; the water, therefore, enters by the 

 gaping mouth, and rushes through the sieve-like interspaces of the 

 branchial arches into the branchial cavity ; the mouth then shuts, 

 the opercular doors press upon the branchial and hyoid archus, which 

 again advance forwards, and the branchiostegal membranes being 

 withdrawn, the currents rush out at tlie open po.sterior branchial 



