392 MERISTIC VARIATION. [part i. 



it is the external ' which is the greater, being in several cases a three- 

 phalanged digit shaped like an index (see No. 486). Nevertheless in the 

 Fowl it is the internal which is the greater. 



The conditions in the following cases are not far removed from those named 

 above. 



593. Archibuteo lagopus (Rough-legged Buzzard) : specimen in good condition 

 shot near Mainz, being otherwise normal. The toes of the left foot were placed as 

 usual in a bird of prey, but on the outside 2 of the hind toe was a much smaller 

 accessory toe. This accessory toe was attached to the hind toe almost as far as the 

 base of the claw of the latter. The claw of the accessory toe was half the size of 

 that of the hind toe. In the left leg the muscles of the thigh arid shank were less 

 developed than usual. Toes of right foot abnormally arranged, being all directed 

 forwards. The three normally anterior toes were on the inside of the series, and 

 the toe which should properly be single and directed posteriorly was double and was 

 directed anteriorly. These abnormally disposed toes were not functional. The 

 right leg was much more developed than the left, and it seemed as if the bhd had 

 habitually stood on the right leg. von Reichenau, W., Kosmos, 1880, vn. p. 318. 



594. Gallinula chloropus (Moorhen): specimen killed in Norfolk in 1846. "Each 

 of the hind toes possessed a second claw, which in the right foot merely springs 

 from about the middle of the true toe, but in the left is attached to a second toe, 

 which proceeds from the original one, about half-way from its junction with the 

 tarsus." Extra toe and claw in each case attached outside*- of the true hind toe. 

 Gurnet, J. H., and Fisher, W. E., Zoologist, 1601. 



Guinea-ben having double hallux ; of the two digits the external - was the 

 longer. Geoffroy St Hilaire, Hist, de Anom., i. p. 695. 



Division of digits II and III. 



595. Anas querquedula, L. (Garganey Teal): wild specimen having the left foot 

 abnormally formed. In it there was no toe occupying the place of the hallux, but 

 the digits II and III [using the common nomenclature] were partially bifurcated. 

 In the digit III, the extremity only was divided, but each part bore a separate nail 

 and there was no web between these secondary digits, which were somewhat irregular 

 in form. The digit II divided in about its middle into two nearly similar digits, 

 which were united by a web. The nails of these digits were hypertrophied. Erco- 

 lani, Mem.. Ace. Bologna, S. iv. T. rn. p. 804, Tav. ui.Jig. 1. 



596. (4) From the condition seen in (3) it might be supposed that 

 duplicity of the hallux is the least possible step in the progress of the 

 four-toed form towards the five-toed. It is only one of the least possi- 

 ble steps. For in a few cases upon the base of the digit recognizable 

 as the hallux, and standing in the normal place of the hallux, may be 

 found a minute rudiment of a digit, sometimes with a nail, sometimes 

 without. Between this and the well-formed fifth toe all conditions exist. 



There are thus, as usual in the numerical variations of Meristic 

 Series, two least conditions, one being found in duplicity of a single 

 member, the other taking the form of addition of a rudimentary 

 member beyond the last member. 



597. Passing now from the simpler conditions of the variation to the 

 more complex, several distinct states may be mentioned. The diverg- 

 ence from the normal may be greater either by the presence of two 

 extra digits, or by change in the position of the extra digit or digits. 



1 The only case to the contrary is that mentioned by Windle, Jour. Anat. Phys , 

 xxvi. p. 440, in which a three-phalanged digit stood on the radial side of a pollex. 

 This case has not been described. See pp. 326 and 352. 



2 In reading these records it should be remembered that owing to the backward 

 direction of the hallux the apparent outside is morphologically inside, and probably 

 this is meant in each case. 



