CHAP. XIII.] 



DIVISION OF DIGIT : HORSE. 



369 



unciform, but in its stead, the head of the outer metacarpal was continued upwards 

 to articulate with the cuneiform. Between the heads of the two metacarpals was 

 an irregularly quadrate bone which articulated with the magnum in the place where 

 the large metacarpal (III) should be. This bone however only extended a little 

 way, articulating at its outer end with a notch in the external metacarpal. [This is 

 the author's view, but the figure strongly suggests that this quadrate bone may have 

 been originally in connexion with the external metacarpal and that it may have been 

 separated from it by fracture. If this were so, the large metacarpal would then not 

 be represented by a separate bone at all.] The outer metacarpal distally bore three 

 phalanges of irregular shape, Hexed backwards and outwards. The inner metacarpal 

 articulated solely with the trapezoid. Peripherally it bore a callosity which was 

 due to the healing of a fracture. The phalanges of the inner metacarpal were three, 

 but the first was reduced in length, while the second was elongated and bent in a 

 sinuous manner. The ungual phalanx of this toe was cleft. [The author 

 regards this case as analogous to the foregoing one, No. 544, that is to say, as an 

 instance of development of the normally rudimentary lateral metacarpals to the 

 exclusion of the large one (III), and he considers therefore that the large metacarpal 

 (III) is only represented by the quadrate ossification which lay between the two 

 developed metacarpals.] Ercolani, G. B., Mem. delta Ace. Set. d. Istituto di 

 Bologna, S. 4, T. in. 1881, p. 760, Tav. i.fig. 11. 



Foal in which the feet were all very abnormal. In the two fore feet the meta- 

 carpal of the normal toe (III) was very little developed, being however somewhat 

 larger on the left side than it was on the right. It bore no digit. The external 

 metacarpal bone (IV) of each fore foot attained a considerable length and bore a 

 small hoof-bone. In the left fore foot the inner metacarpal was present but reduced ; 

 in the right foot it was absent. Right hind foot also had the external metacarpal 

 developed and bearing three small phalanges, but the central metacarpal (III) was 

 fairly developed, bearing however only two phalanges. Left hind foot was amor- 

 phous. Boas, J. E. V., Deut. Ztschr. f. Thiermedecin, vn. pp. 271—275. [For full 

 description, measurements and figures see original.] 



B. Cases in which metacarpal III gives articulation to 



MORE THAN ONE DIGIT. 



These cases are clear examples of the representation of a single 

 digit by two. It will be seen besides that the 

 two resulting digits may stand to each other 

 in the relation of optical images (see Fig. 110) 

 and do not form a Successive Series, thus 

 following the common method of division of 

 structures possessing the property of Bilateral 

 Symmetry in some degree (cp. p. 77). All 

 cases of this variation known to me occurred 

 in the fore limb. 



Foal : a right fore foot figured from a specimen 

 in. the collection of the Veterinary School of 

 Copenhagen (Fig. 110) has two complete digits 

 articulating with a single normal metacarpal bone. 

 The two digits are symmetrically developed ; each 

 consists of three phalanges and bears a hoof. 

 These two hoofs are well formed 

 wards each other like those of 

 Boas, J. E. Y., Deut. Ztschr. f. 

 vn., p. 277, Taf. xi., fig. 9. 



Two fore feet of a foal, each being irregularly 

 and unequally bifid. Boas, ibid., figs. 7 and 8. 



inl 



and curve to- 



Artiodactyles. 



Thiermedecin, 



Fig. 110. Right 

 fore foot of Horse No. 

 547. 



Mcp, peripheral 

 end of metacarpal III. 

 ext, external side, int, 

 internal side. 

 (After Boas.) 



24 



