Professor Owen's Teleology of the Skeleton of Fishes. 223 



orifices. These functions are the true condition of the high develop- 

 ment of those hyoides in fishes. 



I have noticed the great development, the persistence, and ossifi- 

 cation of the branchial arches in connection with the transitory ma- 

 nifestation of cartilaginous branchial arches in the larvae of the 

 Batrachia ; this is one of those similarities that has led to the me* 

 taphorical expressions of " gigantic tadpoles," as applied to fishes. 

 But we see how admirably the branchial arches are adapted to the 

 aquatic respiration of the fish, by their advance to a grade of de- 

 velopment, which they are never destined to attain in the frog. 

 Observe their firm ossification, their elastic joints, the sieve-like 

 valves developed from the side next to the mouth, prearranged 

 with the utmost complexity and nicety of adjustment to prevent the 

 entry of any particle of food or other irritating matters into the in- 

 terspace of the tender, highly vascular, and sensitive gills. Observe, 

 also, how the last pair of these arches is reduced to the capacity of 

 the pharynx which it surrounds, how it is thickened in order to 

 support teeth of multiform character, according to the nature of the 

 food ; in short, converted into an accessory pair of jaws, and the 

 most important of the two. In no other Vertebrate anirhals is the 

 mouth provided with maxillary instruments at both fore and hind 

 apertures ; in no other part of the ichthyic organization is the spe- 

 cial divergence from any conceivable progressive scale of ascending 

 structure culminating in Man so plainly marked as this is. 



All writers on Animal Mechanics have shewn how admirably the 

 whole form of the fish is adapted to the element in which it lives 

 and moves ; the viscera are packed in a small compass, in a cavity 

 brought forwards close to the head ; and whilst the consequent abro- 

 gation of the neck gives the advantage of a more fixed and resisting 

 connection of the head to the trunk, a greater proportion of the 

 trunk behind is left free for the development and allocation of the 

 muscular masses which are to move the tail. In the caudal which, 

 is usually the largest portion of the trunk, transverse processes cease 

 to be developed, whilst dermal and intercalary spines shoot out from 

 the middle line above and below, and give the vertically extended, 

 compressed form, most efficient for the lateral strokes, by the rapid 

 alternation by which the fish is propelled forwards in the diagonal 

 between the direction of these forces. The advantage of the bicon- 

 cave form of vertebrae with intervening elastic capsules of gelatinous 

 fluid in effecting a combination of the resilient with the muscular 

 power, is still more obvious in the Bony Fishes than in the shark. 



You may be reminded that all the vertebrae of the trunk are dis- 

 tinct from one another at one stage of the quadruped's develop- 

 ment, as in the fish throughout life ; and you might suppose that 

 the absence of that development and confluence of certain vertebrae 

 near the tail, to form a sacrum, was a mark of inferiority in fishes, 

 3ut note what a hinderauce such a fettering of the niovenients of 



