METAMORPHOSES OF THE FROG's SKELETON. 67 



tilage at the end of this supports two short terminal rays. 

 This is the pattern of the subdivision of the appendage 

 both of the scapular and pelvic arches, in all the higher 

 vertebrates ; hence, in consequence of the vast modifica- 

 tions of the several segments, the necessity for their 

 special names. In the fore-limb the first segment (Fig. 

 83), 53, is the " arm," and its bone, the " humerus," No. 

 63 ; the second segment is the forearm — its two bones 

 are the "radius," No. 55, and "ulna," No. 54; the third 

 segment is the " hand" — its rays are the " fingers ;" and 

 its bones are subdivided into " carpals," No. 56, " meta- 

 carpals," and "phalanges," No. 57. In the hind-limb 

 (Fig. 34), the first segment is the " thigh," and its bone, 

 the " femur," No. 65 ; the second segment is the " leg," 

 and its two bones are the " tibia," No. QQ^ and " fibula," 

 No. 67; the third segment is the " foot" — its rays are the 

 "toes;" its bones are subdivided into "tarsals," "meta- 

 tarsals," and " phalanges." 



In the siren, the pelvic arch and limbs are not de- 

 veloped; but they coexist with the scapular arch and 

 limbs in all other batrachia. In the proteus, the last seg- 

 ment of the fore-limb divides into three rays, that of the 

 hind-limb into two rays ; in other words, it has three 

 fingers and two toes. The menobranchus has four fingers 

 and four toes. The axolotl has four fingers and five toes. 

 The menopome has five fingers and five toes. 



The ultimate subdivisions of the radiated or diverging 

 appendages of the scapular and pelvic arches do not ex- 

 ceed five in any existing air-breathing animal, and their 

 further complexity is due to the specialization of each 

 digit, so as to combine in associated action, instead of 

 their indefinite multiplication, which causes the seeming 

 complexity of the same appendages in fishes. 



