372 



MERISTIC VARIATION. 



[part I. 



metry of the limb complementary to the larger digit. It is a 

 partial substitute for the inner half of the digit III. If the 

 visible Symmetry of the limb is an index of mechanical relations 

 in which the parts stood to each other in the original division of 

 the manus into digits it is possible that there may have been 

 a mechanical equivalence between the two digits. 



554. Mule (between jackass and mare): foetus of about nine months having super- 

 numerary digits. Hind limbs normal. Fore limbs normal as far as peripheral 

 ends of metacarpals. Each manus consisted of three digits. Eight. Metacarpals 

 II and IV normal splint-bones. Metacarpal III normal as far as line of union with 

 its distal epiphysis. The inner part of the sheath of the epiphysis is continued into 

 a rod of fibro-cartilage which supports an extra toe. This rod of cartilage contains 

 a small ossification which represents, as it were, the proximal phalanx of this 

 internal supernumerary toe. Its outer end bears a small second pbalanx, and this 

 bears a small distal phalanx which was covered by a hoof. This extra toe, therefore, 

 is internal to the main continuation of the leg, commences from the line of union 

 between the large metacarpal and its epiphysis, and has three phalangeal joints. 



The epiphysis of the large metacarpal supports a normal first 

 phalanx with which the second phalanx articulates. This 

 second phalanx is enlarged iuternally [details obscure] to 

 bear a small extra nodule of cartilage which appears to be 

 of the nature of an extra toe. The second phalanx also 

 bears a large third (ungual) phalanx. This ungual phalanx 

 together with the minute supernumerary toe borne by the 

 second phalanx are together encased in a common hoof, but 

 the hoof is divided by a groove into two distinct lobes, 

 corresponding with the division between the two digits 

 which it contains. The whole foot, therefore, has one free 

 internal toe and one large toe bearing a small internal one, 

 which are enclosed in a common hoof. 



Left fore foot. Fig. 113. The small, lateral metatarsals 

 II and IV, and the large central metatarsal III are normally 

 constructed ; but from the inner side of the sheath of the 

 large metatarsal, upon the line of union between the bone 

 and its epiphysis, arises a fibro-cartilaginous rod, which 

 contains an ossification representing the proximal phalanx 

 of a supernumerary toe (lettered II in fig.). This rod of 

 tissue in its proximal portion is represented in the figure as 

 abutting on, but distinct from the end of the inner small, 

 lateral metatarsal. It bears a cartilaginous second phalanx, 

 containing a small ossification, which articulates with a 

 terminal (ungual) phalanx covered by a hoof. 



The distal end of the large metatarsal articulates with 



a large first phalanx, which at its proximal end is of normal 



width. At about its middle point this phalanx bifurcates 



into two parts, of which the inner, Ilia, is short and ends a 



little beyond the point of bifurcation : it bears an ungual 



phalanx only, which is encased in a hoof. The outer iimb 



(III b) of the bifurcated first phalanx bears an elongated 



second phalanx of somewhat irregular shape which carries a 



larger ungual phalanx covered by a separate hoof. In this 



foot, therefore, there is an inner toe consisting of three 



phalanges attached to the inside of the large metatarsal : next, 



the proximal phalanx of the large toe is divided longitudinally into two parts, 



bearing (1) an internal toe having only the ungual phalanx and hoof; (2) an outer 



toe which has a second and third (ungual) phalanx. 



In the case of both feet, the hoof and ungual phalanx of the outer toe are turned 

 inwards, having an external curved edge and an internal straight edge; but the two 

 inner toes in each case are turned outivards, having their outer edges straight and 

 their inner edges curved. Jolt, A. et Lavocat, N., Mem. de VAc. des Sci. de Tou- 

 louse, S. 4, Tome in., 1853, p. 364, Plates. [Authors regard this case as proof of 



Fig. 113. Left 

 fore foot of Mule No. 

 554. 



IV, the external 

 splint-bone. Ill, the 

 chief metacarpal. 

 Ilia, Illb, internal 

 and external rudi- 

 mentary digits borne 

 by HI. II, a super- 

 numerary digit at- 

 tached to the inner 

 side of III. 



(After Joly and 

 Lavocat.) 



