The =tarsus= consists of eight small bones arranged in a proximal row of three, the =tibiale=, =intermedium= and =fibulare=, and a distal row of four =tarsalia=, with one bone, the =centrale= (fig. 23, A, 7), interposed between the two rows. In the specimen examined, the =tibiale=, is a small bone articulating with the tibia, the =intermedium= (fig. 23, A, 5) is larger and articulates with both tibia and fibula, the =fibulare= is the largest of the three and articulates with the fibula. The bones of the distal row are =tarsalia 1=, =2=, =3=, and a bone representing =4= and =5= fused. In the specimen examined tarsale 1 is pushed away dorsally (fig. 23, A, 8), so as to lie between the tibiale and tarsale 2. All the tarsal bones are small and somewhat polygonal, and are connected with one another, and with the tibia and fibula on the one hand, and with the metatarsals on the other by a thin layer of cartilage. The five =digits= of the foot each consist of a =metatarsal= and of a certain number of =phalanges=. In the specimen examined, owing to the shifting of tarsale 1, the first metatarsal as well as the second articulates with tarsale 2, while the fifth metatarsal articulates partially with the bone representing the fused tarsalia 4 and 5, partially with the fibulare. All the bones of the digits except the distal phalanges are terminated at each end by cartilaginous epiphyses, the distal phalanx of each digit has a cartilaginous epiphysis only on its proximal end. The first, second, and fifth digits have two phalanges apiece, the third and fourth have three. Figure 31 B, showing a Newt's tarsus copied from Gegenbaur, has precisely the arrangement generally regarded as primitive for the higher vertebrates, except that tarsalia 4 and 5 are fused. FOOTNOTES: [54] i.e. between one vertebra and the next. CHAPTER XI. THE SKELETON OF THE FROG[55] (_Rana temporaria_). I. EXOSKELETON. The skin of the frog is smooth and quite devoid of scales or other exoskeletal structures. The only exoskeletal structures met with in the frog are:-- 1. The =teeth=, which are most conveniently described with the endoskeleton. 2. The horny covering of the calcar or prehallux (see p. 167). II. ENDOSKELETON. The endoskeleton of the adult frog consists partly of cartilage, partly of bone and each of these types of tissue occurs in two forms. The cartilage may be hyaline, as in the omosternum and xiphisternum, or may be more or less calcified as in part of the suprascapula and the epiphyses of the limb bones. The bone may be cartilage bone, or membrane bone. The skeleton is divisible into an =axial portion= consisting of the skull, vertebral column, and sternum, and an =appendicular portion= consisting of the skeleton of the limbs and their girdles. 1. THE AXIAL SKELETON. A. THE VERTEBRAL COLUMN.