314 MERISTIC VARIATION. [part I. 



Hind foot. 



The phenomena seen in the case of the hind foot are in some 

 respects simpler than those of the variations in the fore foot, and 

 for this reason they may conveniently be described first. 



If the phalanges of the index of the hind foot, for example, be 

 examined, it will be seen that the proximal phalanx is nearly 

 bilaterally symmetrical about a longitudinal axis, but that the 

 second phalanx is deeply hollowed out upon the external or fibular 

 side. Into this excavation the ungual phalanx is withdrawn when 

 the claw is in the retracted position. The retraction is chiefly 

 effected by a large elastic ligament running from the outside of 

 the distal head of the second phalanx and inserted into the upper 

 angle of the last phalanx (see Owen, Anat. and Phys. of Vert., in. 

 p. 70, fig. 36). The same plan is found in the digits II to V both 

 of the fore foot and of the hind foot. By this asymmetrical re- 

 traction of the claw a digit of the right side may be differentiated 

 at a glance from one of the left side, for the claw is retracted to 

 the right side of a right digit and to the left side of a left digit. 

 The importance of this fact will be seen on turning to the evidence, 

 for it is found that with variation in the number of digits there is 

 a correlated variation in their symmetry. 



With respect to the tarsus little need be said. The proximal 

 part of the tarsus contains three bones, the calcaneum, astragalus 

 and navicular. The distal row consists of four bones, the cuboid 

 and three cuneiform bones. In the majority of polydactyle cats 

 that I have seen in which the tarsus is affected, the cuboid is 

 normal and the ecto-cuneiform is also normal and recognizable ; 

 internal to the latter there are three small cuneiforms articulating 

 with the navicular instead of two, making four cuneiforms in all. 

 In some specimens there is no actual separation between the two 

 innermost of these cuneiforms, but the lines of division between 

 them are clearly marked. 



In the normal hind foot of the Cat there are four fully formed 

 toes, commonly regarded as II, III, IV and V, each having 

 three phalanges. In the place where the hallux would be there 

 is a small cylindrical bone articulating at the side of the internal 

 cuneiform. As usually seen, all the four digits are formed on a 

 similar plan, each having its claw retracted to the external or 

 fibular side of the second phalanx, the four digits of a right foot 

 being all right digits and those of left feet being all left digits. 

 The rudimentary hallux has of course no claw. 



Starting from this normal as the least number of digits, it will 

 be found that a large proportion of cases are such that they may 

 be arranged in an ascending or progressive series. In this series 

 the following Conditions have been observed. 



In the schematic representations of the limbs the words 'Eight' or 'Left' 

 signify that a digit is shaped as a right or as a left. The Roman numeral 



