THE ANTERIOR LIMBS. 123 



—such as the 3Ioh, Marmot, and Guinea-pig— each, of which have five digits 

 arising from the two carpal bones. In order to study the hand, these authorities 

 place it in its natural position — pronation ; and the different pieces are reckoned 

 from without to within by the numbers 1, 2, 3, 4, 5. 



3. Modifications in the Archetype. But the archetypal hand is not 

 constantly realized, even when five digits— such as they are usually understood 

 to be — are present. The hmnan hand, for instance, is formed by five digits and 

 five metacarpal bones, with only eight bones in the carpus. When we go from 

 Man, the number of bones in the three sections is more or less diminished ; and 

 in the carpus of the domestic animals, as in that of Man, if the archetypal 

 number does not exist in all the sections, it is because certain pieces have been 

 fused with adjoining ones, or they are not developed. In several instances, 

 certain bones become so atrophied that at the first glance they are not recog- 

 nizable. Joly and Lavocat at first imagined that these atrophies took place 

 according to some fixed law ; they believed that the atrophy operated on the 

 middle part of the bones, extending downwards, and that the last piece to dis- 

 appear, in an atrophied digit, was that of the carpus. 



But since the publication of their first memoires, Lavocat has had occasion 

 to state that this law is not absolute. After these preliminary remarks, we 

 will study the modifications in the archetypal hand in Man and the domestic 

 animals, and demonstrate that in these it may easily be referred to the pentadacty- 

 lous type. 



1. Man. — The human hand having five digits and five metacarpal bones, it 

 is rational to admit the virtual existence of five pieces to each of the carpal rows. 

 Materially, there are only four bones in each of these two rows ; but the com- 

 parative study of the relations of each of these bones in the human carpus, and 

 in that of animals which are in possession of the archetypal hand, leads to the 

 belief that the scaphoid is the result of fusion of the fourth and fifth bones of 

 the upper row, and the unciform the fusion of the first and second bones of the 



HAND OF MAN AND THE DOMESTIC MAMMALIA, NORMAL AND TERATOLOGICAL (Fig. 82). 



A, Human hand (dorsal face). 



B, Dog's hand (same position). 



C, Pig's hand (normal condition). 1, Trapezium. 



c', Pig's hand : the thumb (1) is completely developed from the trapezium (2). 



D, Sheep's hand (normal condition). 1, Principal metacarpal ; 2, rudimentary metacarpal, external ; 

 3, ditto, mternal (not constant). 



E, Hand of the aquatic Chevrotain. 1, Double principal metacarpal; 2, 3, lateral metacarpals 

 followed by phalanges. 



F, Lamb's hand, a. Carpus and superior extremity of metacarpus (seen in profile), on which the 

 metacarpus of the thumb (1) was shown. 6, Ditto (face) : 1, internal rudimentary metacarpal 

 completely developed ; 2, horny plate representing the thumb on the surface of the skin ; 3, horny 

 plate representing the first digit on the surface of the skin. 



G, Lamb's hand on which are four complete digits. 1, Principal metacarpal ; 2, 3, lateral meta- 

 carpals completely developed. 



H, Horse's hand (normal condition). 1, Principal metacarpal ; 2, 3, rudimentary metacarpals. 



I, Horse's hand, adult (teratological specimen, showing the division of the phalangeal section, 

 1, 1, of the single digit of Solipeds). 



K, Foal's hand (teratological specimen described by Delplanque). 1, Principal metacarpal bifid in 

 its lower third ; 2, e.\ternal rudimentary metacarpal ; 3, 4, phalangeal sections resulting from 

 the division of the great digit. 



L, Horse's hand, adult (teratological piece), a. Carpus (inner aspect) : 1, trapezium ; 2, trapezoid ; 

 3, principal metacarpal ; 4, internal rudimentary metacarpal transformed into a complete meta- 

 carpal ; 5, styliform piece representing the metacarpal of the thumb. 6, Inferior extremity of 

 the digital region (inner aspect): 1, principal metacarpal, followed by normal phalanges; 2, in- 

 ternal rudimentary metacarpal transformed into a complete metacarpal, followed by normal 

 phalanges. 



