The =tarsus= consists of two rows of structures, very different in size. The proximal row consists of two long bones, the =tibiale= and =fibulare=, which are united by common epiphyses at the two ends, while in the middle they are widely separated. The tibiale lies on the tibial or pre-axial side, and the fibulare which is the larger of the two bones on the fibular or postaxial side. The distal row of tarsals consists of three very small pieces of calcified cartilage. The postaxial of these is the largest, it articulates with the second and third metatarsals and is probably homologous with tarsalia 2 and 3 fused. The middle one is very small, it articulates with the first metatarsal and is probably tarsale 1. The pre-axial one articulates with the metatarsal of the calcar, a structure to be described immediately, and has been regarded as a =centrale=. The =foot= includes five complete digits and a supplemental toe as well. Each of the five digits consists of a long =metatarsal= with epiphyses at both ends, and of a variable number of phalanges. The first digit or =hallux= and the second have two phalanges, the third three, the fourth, which is the largest, four, and the fifth, three. The distal phalanges have epiphyses only at their proximal ends, the others at both ends. On the pre-axial side of the hallux is the supplemental digit, the =prehallux= or =calcar=. It consists of a short metatarsal and one or two phalanges, and is terminated distally by a horny covering of epidermal origin. FOOTNOTES: [55] See A. Ecker, _Die anatomie des Frosches_, Braunschweig 1864, translated by G. Haslam, Oxford, 1889, also A.M. Marshall, _The Frog_, 5th edition, Manchester and London, 1894. [56] W.K. Parker, _Phil. Trans._ 161, 1871, p. 137, and W.K. Parker and G.T. Bettany, _The Morphology of the Skull_, London, 1877, p. 136. [57] See G.B. Howes and W. Ridewood, _P.Z.S._, 1888, p. 141. [58] See bottom of p. 187. CHAPTER XII. GENERAL ACCOUNT OF THE SKELETON IN AMPHIBIA. EXOSKELETON. The exoskeleton, at any rate in most living forms, is very slightly developed in Amphibia. The only representatives of the epidermal exoskeleton are (1) the minute horny beaks found coating the premaxillae and dentaries in _Siren_ and the tadpoles of most Anura, (2) the nails borne by the first three digits of the pes in _Xenopus_ and by the Japanese Salamander _Onychodactylus_, (3) the horny covering of the calcar or prehallux of frogs. The Urodela and nearly all the Anura, which form the vast majority of living Amphibia, have naked skins. A few Anura belonging to the genera _Ceratophrys_ and _Brachycephalus_ have bony dermal plates developed in the skin of the back, and these plates become united with some of the underlying vertebrae. In the Gymnophiona the integument bears small cycloid scales arranged in rings which are equal in number to the vertebrae. These scales contain calcareous concretions. Scales also occur between the successive rings.