390 MERISTIC VARIATION. [part i. 



these bones are completely fused together ; and, further, a third ossicle was developed 

 at their proximal ends, where they are not completely united, between and above 

 them " [cp. No. 587]. " It might have been imagined that the deformity was simply 

 the result of an agglutination along the middle line of the two completely-formed 

 digits ; but such is not the case, the nail-structure being absent in the interval, 

 where it is replaced by bone with a transverse cartilage below it. The nail is con- 

 tinued straight across the middle line of the hoof, as in the horse." Gaeeod, A. H., 

 Proc. Zool. Soc, 1877, p. 33. 



587. Domestic pigs having the two central hoofs compounded into a single solid hoof 

 have been known to occur several times in America. The two other toes remain 

 distinct in these cases. A breed of pigs having this character is said to have been 

 established in Texas, which transmits this peculiarity in a definite way. In this 

 breed the peculiarity is said to have been so firmly established that "no tendency to 

 revert to the original and normal form is observable in these pigs." A cross between 

 a solid-hoofed boar and an ordinary sow is said to produce a litter of which the 

 majority shew the peculiarity of the male parent. " On the sole of the hoof, there 

 is a broad, angular elevation of horny substance, apex forward, and sides running 

 backward and outward to the lateral borders of the hoof, the whole structure being 

 curiously like the frog of the horse's hoof. In fact it is a frog, though broad, 

 flattened, and somewhat horseshoe-shaped, instead of being narrow, deep and acute 

 as in the actual frog of the horse. This arcuate thickening of the corneous sub- 

 stance occupies about the middle third of the whole plantar surface of the foot." 

 The terminal phalanges are united together, and above this single bone is another 

 independent ossification lying between the second phalanges of the two digits, which 

 remain distinct. [Cp. No. 586.] Coues, Elliott, Bull. U. S. Geol. Geogr. Surv., iv. 

 P- 295, fig. 



588. Case resembling the above reported from Sioux City, Iowa, in which these pigs 

 were bred for some time and were advertised for sale, with the statement that they 

 were also of superior quality. Other cases given from different parts of the United 

 States. In one of these it is stated that one hind foot was thus formed [the others 

 being presumably normal]. Auli>, E. O, Amer. Nat., 1889, xxin. p. 447, fig. 



589. Tig- In all four feet the digits III and IV partially united and covered by one 

 hoof. The metacarpals and first phalanges were separate in each case but the 

 second and third phalanges of the two digits were united together. The common 

 hoofs were not compressed laterally, as in some of the cases seen in the Calf, and 

 the small digits II and V were unmodified. Kitt, Dent. Zt. f. Thierm., xn. 1886, 

 Jahresb., 1884-85, p. 64, Case TV, figs. 



POLYDACTYLISM IN BlRDS 1 . 



The whole number of cases of Polydactylism recorded in 

 birds generally is small. The phenomena however seen in the 

 Dorking fowl are well worthy of attention and have scarcely been 

 adequately treated. I propose here to give an account of this 

 case, mentioning instances seen in other birds and indicating so far 

 as may be their relation to the facts of the Dorking. 



Five-toed fowls have been known from very early times. The 

 character is now most definitely associated with the Dorking, though it 

 is also considered necessary in Houdans for show purposes. It is 

 likely that the latter breed derived the fifth toe from the Dorking. 

 Fifth toes may often be seen to occur in other breeds, but I cannot 

 quote a satisfactory record of their appearance in pure strains. 



In the foot of an ordinary four-toed fowl the hallux articulates with 

 the tarso-metatarsus by a separate metatarsal. The hallux in such a 

 foot most often has two phalanges. In its commonest form the five- 

 toed foot departs from this normal in the fact that the hallucal meta- 



1 See also the case of Rissa, p. 396. 



