go6 



SUB-KINGDOM VERTEBRATA. 



directly with the periotic region ; but in the greater number of 

 Fishes the mandible, as already mentioned, is connected with the 

 cranium by means of the hyomandibular suspensorium (fig. 823). 

 Having now noticed the leading features of the axial, we may 

 proceed to an equally brief survey of those of 

 the appendicular skeleton. In all the higher 

 Vertebrates the limbs are divided into three 

 sections — viz., in the pectoral or fore limb 

 the arm, fore-arm, and the hand or manus ; 

 and in the pelvic or hinder limb the thigh, leg, 

 and the foot or pes. The first segment has a 

 single bone — the humerus of the arm, and the 

 /--■■ll fernur of the thigh (fig. 828); the second has 



two parallel bones — the radius and ulna in 

 the fore-arm, and the tibia and fibula in the 

 leg (fig. 828); while the third segment con- 

 tains a number of bones arranged in not more 

 than five longitudinal rows (figs. 828, 829), 

 with the exception of the Ichthyopterygian 

 Reptiles. The bones of the manus and pes 

 are again divisible into three sections — -viz., 

 proximally the carpus or wrist in the manus 

 (fig. 829), and the tarsus or ancle in the pes ; 

 mesially the metapodium, or metacarpus of the 

 manus (fig. 829), and the metatarsus of the 

 pes (fig. 828); and distally the phalangeals 

 (figs. 828, 829) of the digits. With the ex- 

 Fig. 828. — Dorsal aspect ception of the Ichthyopterygia, where the 



of right innominate and , , . . . ......... .. 



pelvic limb of the Chim- normal digits appear to have divided, in all 

 duced! ^^nSin2te; r >; known forms the number of functional digits 

 Femur ; t, Tibia ; s, Fibula .; d oes no t exceed five ; and these are enum- 



r, 1 arsus ; m, Metatarsus ; /, ' ... . 



Phalangeals. (After Owen.) erated consecutively from the radial or tibial 

 side, so that the pollex or thumb of the manus, 

 and the hallux or great toe of the pes are always termed the first, 

 and the little finger and toe the fifth digits. Except in the hallux 

 there are usually not less than three phalangeals in each digit 

 of the pes, but their number may be reduced in the manus. The 

 bones of the metapodium correspond in number with the digits, 

 and consist of a single transverse row. 



Although, as we have stated, the number of digits in the higher Ver- 

 tebrates is typically five, yet there appears to be considerable evidence 

 that the number was originally seven. Thus in many pentedactylate 

 Mammals, and also in some Reptiles and Amphibians, there is found 

 on the radial or preaxial border of the carpus or tarsus a small ossification 

 which Dr Bardeleben terms the prepollex, or prehallux, and regards as 



