SKELETON. 



663 



(fig. 483.) are alike as to those segments 

 which constitute them one and all. Those 

 segments are the scapula (a, a), the humerus 

 (b, b), the fore-arm bones (c, d), the carpal 

 ossicles (e,f), and the metacarpo-phalangeal 

 series (1, 2, 3, 4, 5). Every species of the 

 fore member produces these segments in- 

 variably ; I say invariably, for I am not now 

 referring to their pathological state. 



When I compare all fore-limbs by the 

 scapula (a) or proximal segment, I find that 

 this bone is invariably present, though very 

 much modified in several animals. As all 

 scapulary organs of mammals, birds, reptiles 

 (and I would add the osseous fishes, but for 

 certain facts which require previous expla- 

 nation,) produce the bone named scapula, 

 they may be hence termed uniform as to this 

 particular. The invariable occurrence of the 

 humerus (b) renders them likewise uniform 

 as to this segment. But though the fore-arm 

 carpus and metacarpo-phalangeal segments 

 are, as segments, invariably present likewise, 

 still all fore-limbs are not equal or uniform as 

 to the quantity contained in each of these 

 segments. Considering the fore-limbs under 

 general notice, I see that they are uniform by 

 the proximal ends (, b) of the organs, and 

 variously by the distal or terminal appen- 

 dages. But it is most true, nevertheless, that 

 this variety is only quantitative, or simply a 

 plus and minus variation, for A produces five 

 digits, B four, c three, D two, and E only one. 

 Of the two bones (c, d] constituting the 

 fore-arm, that one which is most constantly 

 developed in entire proportions is the ra- 

 dius (<?), The ulna (d) is very often reduced 

 to almost unrecognisable dimensions (d of E) ; 

 and that part of the ulna which is most gene- 

 rally metamorphosed or annihilated is its 

 distal or carpal extremity. The olecranon 

 process and a part of the shaft of the ulna is 

 always present. 



The carpal ossicles (>,/), which in all fore- 

 limbs manifest a greater relationship to the 

 radius (c) than to the ulna (d), are as constant 

 as the radius itself. The metamorphosis of 

 the ulna {d of E) does not appear to affect 

 the carpal ossicles (e,f). 



The metacarpal bones (Jig. 483.) are nu- 

 merically various in these scapulary organs. 

 Though it be true that we find them in all 

 fore-limbs, still we do not find them produced 

 in equal numbers. The metacarpal bones are 

 not constant to the number of five ; but 

 though we find them varying in a plurality of 

 animals from the number of 5 in A to that of 

 1 in E, still we should not overlook the fact, 

 that in certain fore- limbs, as D and E, where, 

 to all appearance at first sight, a single meta- 

 carpul bone is developed, a closer inspection 

 will prove that others may be present, though 

 in rudimental form (5 of E). 



The phalangeal ossicles (2, 4, 6, of B, 

 fig. 484.) which constitute a finger are usu- 

 ally three in number ; but there are ex- 

 ceptions to this rule. The fingers themselves 

 are generally found to correspond in number 

 with the metacarpal bones. When there are 



five metacarpal bones, the fingers are five in 

 number also. When animals have only four, 

 or three, or two, or one metacarpal bone 

 (fig. 483.), the fingers number accordingly. 

 There may be more metacarpal bones than 

 there are fingers, but as many of the fingers as 

 are present, whatever be their number, have 

 each invariably a corresponding metacarpal 

 bone. The rudimental metacarpal bones 

 have, generally speaking, rudimental pha- 

 langes. 



The thumb varies as to the number of its 

 phalanges, and becomes a finger or a thumb 

 according to this occurrence. The meta- 

 carpal bone of the thumb is very often pre- 

 sent when the phalangeal thumb ossicles are ab- 

 sent ; and sometimes I find that some species 

 of animals have only one phalanx for a thumb ; 

 sometimes two, sometimes three. The digit 

 which is a thumb in one animal (fig. 484. B), 

 by reason of the fact that it stands apart from 

 the other digits, is now and then laid side by 



Fig. 484. 



side (A) with the other digits, and becomes a 

 finger accordingly. I have reason to believe 

 that the bone (1,2, next to 7 of B) which we 

 term metacarpal bone of the thumb in one 

 animal is the true homologue of the first 

 phalanx of the finger appended to 8 of A, 

 and for this reason, viz. that the metacarpal 

 bone of the human thumb (1, 2 appended to 

 7 of B), is constituted of two ossicles, which 

 have become consolidated. If we class the 

 hindmost ossicle (1 of the bone, 1, 2 ap- 

 pended to 7 of B) with the other meta- 

 carpal bones, then the foremost ossicle (2) 

 will represent the first phalanx (2) of the 

 other fingers, and this will give (as in A) three 

 phalanges to the thumb, as to the other 

 fingers. It is worthy of notice, that the so- 

 called metacarpal bone of the thumb (1 , 2 of B) 

 corresponds as to nucleary deposit with the 

 first phalanx (1, 2) of the finger. 



The foregoing mentioned facts respecting 

 the scapulary organs will prove that they are 

 "unity in variety," the unity being a plus 

 quantity (as A, fig. 483. with five digits) ; 

 whereas the variety is simply a minus quan- 

 tity, so rendered by the degradation or meta- 

 morphosis of the quantity of five digits, which 

 u u 4 



