OSSEOUS SYSTEM. (CoMp. ANAT.) 



1341 



fin rays, however numerous, are connected ; 

 with the exception of the first, which articulates 

 immediately with the radius. In some Fishes, 

 as in the Lophius, these bones are extraordi- 

 narily lengthened, while the radius and ulna 

 are diminished in proportionate size; so that 

 some writers have mistaken the bones of the 

 carpus for those of the forearm. 



In the Batrachia, and in all four-footed Rep- 

 tiles, they are small ossicles interposed between 

 the bones of the forearm and metacarpal bones, 

 resembling very much those of the human sub- 

 ject; butin Birds, in consequence of the peculiar 

 condition of the hand, here converted into a 

 wing, they are reduced to two, so disposed as to 

 form with the bones of the forearm a mere 

 hinge-joint moving laterally, so as to allow the 

 wing to be folded up. 



In the Cetacea the carpal bones exist, it is 

 true, but so separated from each other by an in- 

 terposed cartilaginous mass that they assist in 

 forming a broad paddle, strengthened by super- 

 ficial ligaments, and only useful for progression 

 in the water. 



In all other Mammalia the carpal bones are 

 met with, their form and number varying with 

 the uses for which the limb of which they form 

 a part is adapted. 



The metacarpal bones form the immediate 

 basis on which the individual fingers are sup- 

 ported, and, accordingly, are as variable in their 

 number and arrangement as are the digital 

 portions of the anterior extremity. 



In Fishes, owing to the numerous fingers or 

 rays as they are here called, the metacarpal 

 bones are met with in far greater numbers than 

 in animals where the extremities assume a more 

 concentrated form, a fact most remarkably 

 exemplified in the Chondropterygious Fishes, 

 where the number of digital phalanges is enor- 

 mous. But in Reptiles, where the hands are 

 not only reduced to what may be called the 

 normal type of structure, but developed in a 

 medium condition, little remarkable is met 

 with in this part of the hand. It is only as we 

 come to animals appointed to extraordinary 

 conditions of life that aberrations from the 

 usual form become conspicuous, as, for exam- 

 ple, in the feathered races. The metacarpus of 

 Birds, although in some cases it might at first 

 appear composed of a single bone, in others of 

 two bones anchylosed together at both ends, 

 contains, in reality, the elements of three meta- 

 carpal bones consolidated ; two of these, which 

 are much elongated, supporting the fingers, 

 while the third, an exceedingly small element 

 confused with the base of the central one, sus- 

 tains the rudimentary thumb. 



In the metacarpal bones of the unguiculate 

 Quadrupeds there is nothing worthy of notice 

 in this general survey of the osseous system ; but 

 in the Ungulata a coalescence almost as re- 

 markable as in Birds is observable, whereby 

 the peculiar structure of the feet of such animals 

 is provided for. In the Ruminantia and So- 

 lidungula the whole metacarpal apparatus 

 would at first sight appear to consist of a single 

 bone, to which the name of canon-bone is gene- 



rally appropriated ; but this apparently single 

 bone is easily seen to be in reality made up of 

 two, anchylosed together throughout their whole 

 length, so that the line of demarcation between 

 them is only indicated by a deep longitudinal 

 groove, visible on the anterior and posterior 

 aspects of the bone; in most cases, however, 

 there are two more lateral pieces, unattached to 

 the principal or canon-bone except by the soft 

 parts, but evidently real metacarpal elements in 

 an imperfect and rudimentary condition. 



The digital phalanges being the most remote 

 from the central portion of the skeleton are 

 likewise the most variable in number and ap- 

 pearance, being moulded into shapes as various 

 as are the uses to which the anterior limbs are 

 convertible, becoming in turn the framework of 

 oars, of paddles, of pillars, of rakes, of wings, 

 or of hands, in accordance with the different 

 natures of the animals possessing them. Neither 

 is it at all an easy task to say how many of 

 these elements might exist in the construction 

 of this part of the skeleton, seeing that the 

 number of fingers that may enter into the com- 

 position of a hand seems not at all determinate, 

 nor even the number of phalanges in a given 

 finger. The pectoral fins of osseous Fishes, the 

 representatives of the hands of higherVertebrata, 

 differ exceedingly in this respect, sometimes 

 consisting of a single ray, at others being dilated 

 and extended, as in the Flying Fishes, until both 

 rays and phalanges become extremely numerous. 

 The hand or pectoral fin of the Skates is per- 

 haps one of the most remarkable structures 

 that can be offered to the contemplation of the 

 osteologist, whether we regard its apparently 

 disproportionate size or the immense number 

 of digital elements that enter into its composi- 

 tion ; it forms, in fact, the great bulk of their 

 bodies, and is made up of upwards of a hundred 

 distinct fingers, each composed of numerous 

 phalanges of enormous length. Throughout the 

 Serpent tribes all traces of anterior extremities 

 are lost, but in the Anourous Batrachia fingers 

 again appear under a new and more elevated 

 form, although feeble when compared to the 

 digital phalanges of the hinder extremities in, 

 the same Reptiles. 



Throughout the Saurian and Chelonian races 

 as they now exist, nothing remarkable appears 

 in the construction of this portion of the skele- 

 ton, the chief modifications observable being in 

 the number, length, and position of the fingers, 

 although in extinct forms of nearly allied genera, 

 such as the Ichthyosaurus and Plesiosaurus, 

 the number both of toes and phalanges are so 

 prodigiously increased that we are once more 

 reminded of the fins of Fishes. 



The digital phalanges in the wing of a bird 

 are reduced to an exceedingly rudimentary 

 condition, the thumb being represented by a 

 single bone. The central or radial finger is the 

 longest and most complete, consisting, when 

 fully developed, of three distinct joints, though 

 sometimes there are only two. The ulnar or 

 third finger is, like the thumb, represented by a 

 single phalanx appended to the distal extremity 

 of the ulnar ir.etacarpal bone. 



