170 FIRST LESSONS IN ZOOLOGY. 



metacarpals, and the finger-bones or phalanges, the single 

 row of phalanges forming the digit (finger or toe). To the 

 pelvis are attached the hind limbs, consisting each of a 

 femur or thigh, which is succeeded by the tibia and fibula 

 (shank-bones), these being followed by the tarsal and meta- 

 tarsal bones (ankle-bones), and by the phalanges, or bones 

 forming the toes. 



On examining the internal anatomy of the salamander, 

 the most striking difference from fishes is the presence of 

 a pair of lungs. These are long sacks, which somewhat re- 

 semble the air-bladder of a fish ; and, indeed, the lung is 

 the "homologue" or representative of a fish's air-bladder. 

 It will be remembered that the Australian lung-fish has but 

 a single lung, while the African lung-fish has two, which 

 connect by an air-passage with the throat. Some bony fishes 



FIG. 176. Salamander, showing the double row of lateral sense-organs (I l')\ the 

 dots on the head being organs of the same kind. 6, gills. 



have air-bladders divided into chambers, and thus we see 

 that the lungs of amphibians and higher land vertebrates 

 have their beginnings in the air-bladder of fishes. Tad- 

 poles and salamanders also resemble fishes in having similar 

 lateral sense-organs (Fig. 176). 



If now we compare a salamander's skeleton (Fig. 179) 

 with that of a fish (Fig. 138), we shall see some notable 

 differences ; besides the limbs, great changes have taken 

 place in the shoulder and pelvic arches to which the legs are 

 attached ; the bones composing these are more as in the 

 lizards and higher vertebrates, while there is a breastbone 

 or sternum. Moreover, the skull is broad and flat, com- 

 posed of few bones, among which may be distinguished the 

 outer or investing bones of the skull, so well developed in 

 the higher vertebrates ; these are the parietal, frontal, na- 

 sal bones, the vomer, etc. ; still, important parts of the 



