BATRACHIA? 615 



In the tadpole and the genera which retain their gills through life, the sub- 

 stance between the vertebra? is soft, and contained in cup-like hollows formed by the 

 concave articular surfaces of contiguous bones, precisely as in fishes. The lower 

 orders are fish-like in possessing permanent branchiae, the limbs are reduced to a 

 rudimentary condition, and the tail is flattened and surrounded by a fin. In the 

 higher orders the limbs are more and more developed and fitted for terrestrial pro- 

 gression, until they are capable of active motion and the animals can take their 

 habitual residence in trees. The spinal column in some is composed of a continuous 

 chorda dorsalis, inclosed in a fibrous sheath, but furnished with bony superior and 

 inferior arches for the protection of the spinal cord and principal blood-vessels. In 

 others the vertebra? are articulated by a sort of ball-and-socket joint. The verte- 

 bra? are usually furnished with long, transverse processes which appear to take the 

 place of ribs ; ribs are generally deficient. In those having a chorda dorsalis the 

 skull is formed of a simple cartilaginous capsule, with which the chorda is com- 

 pletely continuous, and the only indications of ossification are in the lateral por- 

 tions of the occipital bone. In the higher forms the skull is completely ossified ; it 

 is always of a broad and flattened form, with enormous, large orbits, and possesses 

 one constant character which distinguishes the skull of a Batrachia from that of a 

 Reptile ; namely, the occipital bone is always furnished with two lateral condyles that 

 fit into corresponding sockets in the first vertebra of the neck. The bones of the 

 upper jaw and palate form a broad arch, which is always firmly attached to the 

 skull ; the maxillary and intermaxillary bones assist in the formation of the edge of 

 the mouth, and are much developed, transversely expanding the general form of the 

 skull without involving any enlargement of the brain cavity, which is very small. 



All Batrachia have teeth on the palate ; the salamanders have them also in 

 both the upper and lower jaws, the frogs in the upper only, and the toads in neither. 

 The jaw teeth are always slender, sharp-pointed, and closely set. The frog has 

 about forty on each side of the upper jaw ; the salamander has about sixty above 

 and below ; the palatine teeth are generally arranged transversely parallel to the 

 jaw teeth. The hind legs of the frog are developed for leaping, and it has no use- 

 less tail ; the body is contracted into a short space, and the few vertebra? are united 

 into a single immovable piece, unprovided with ribs. The water salamanders, or 

 newts, have a long tail, a slender flexible body, and all their organs are fitted for 

 aquatic life. The structure of the bones is more compact and calcareous, and less 

 transparent and flexible, than in fishes. The bones of the skull have their margins 

 in contact, and occasionally united, but never overlapping. The hyoid bone changes 

 largely in those genera undergoing metamorphosis in accordance with the develop- 

 ment of the respiratory organ. 



The Batrachia are generally distinguished from the Reptilia by the absence of 

 a scaly covering. The skin of aquatic genera is soft and smooth, and constantly 

 moistened by the cutaneous secretions ; in land genera, as frogs and toads, the glands 

 of the skin secrete a thick, whitish fluid. The cuticle is shed frequently. A few 

 species are covered with horny scales. 



They begin life with the single heart and gills of fishes; but as their metamor- 

 phosis goes on, the heart assumes the compound character necessary for the pul- 

 monary respiration of the reptiles. In the development of the nervous system and 

 the organs of the senses, they exhibit a slight advance upon the fishes. In the first 



