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



the caudal vertebraB would be to creatures which progress by alter- 

 nate vioforous inflections of a muscular tail. A sacrum is a consoli- 

 dation of a greater or less proportion of the vertebral axis of the 

 body, for the transference of more or less of the weight of the body 

 upon limbs organised for its support on dry land ; such a modifica- 

 tion would have been useless to the fish, and not only useless, but a 

 hinderance and a defect. 



The pectoral fins, those curtailed prototypes of the fore-limbs of 

 other Vertebrata, with the last segment, or hand, alone projecting 

 freely from the trunk, and swathed in a common undivided tegu- 

 nientary sheath, present a condition analogous to that of the embryo 

 buds of the homologous members in the higher Vertebrata. But 

 what would have been the effect if both arm and forearm had also 

 extended freely from the side of the fish, and dangled as a bony, 

 flexible, many-jointed appendage in the water \ This higher de- 

 velopment, as it is termed, in relation to the prehensile limb of the 

 denizen of dry land, would have been an imperfection in the struc- 

 ture of the creature which is to cleave the liquid element ; in it, 

 therefore, the fore-limb is reduced to the smallest proportions con- 

 sistent with its required functions ; the brachial and antibrachial 

 segments are abrogated, or hidden in the trunk ; the hand alone 

 projects and can be applied, when the fish darts forwards, prone and 

 flat by flexion of the wrist to the side of the trunk ; or it may be 

 extended at right angles, with its surfaces turned forwards and back- 

 wards, so as to check and arrest more or less suddenly, according to 

 its degree of extension, the progress of the fish ; its breadth may also 

 be diminished or increased by approximating or devaricating the 

 rays. In the act of flexion, the fin slightly rotates, and gives an ob- 

 lique stroke to the water. For these functions, however, the hand 

 requires as much extra development in breadth, as reduction in 

 length and thickness ; and mark how this is given to the so- called 

 embryo or rudimental fore-limb ; it is gained by the addition of ten, 

 twenty, or it may be even a hundred digital rays, beyond the num- 

 ber to which the fingers are restricted, in the hand of the higher 

 classes of Vertebrata. We find, moreover, as numerous and striking 

 modifications of the pectoral fins, in adjustment to the peculiar habits 

 of the species in Fishes, as we do of the fore-limbs in any of tho 

 higher classes. This fin may wield a formidable and special weapon 

 of offence, as in many Siluroid fishes. But the modified hands have 

 a more constant secondary offlce, that of touch, and are applied to 

 ascertain the nature of surrounding objects, and particularly the 

 character of the bottom of the water in which the fish may live. You 

 may witness the tactile action of the pectoral fins when gold fish are 

 transferred to a strange vessel ; their eyes are so placed a« to prevent 

 their seeing what is below them ; so they compress their air-bladder, 

 and allow themselves to sink near the bottom, which they sweep, as it 

 were, by rapid and delicate vibrations of the pectoral fins, apparently 



