2626 



FROGS AND TOADS 



generally but slightly, if at all, developed in the higher Vertebrates, although very 

 large in Fishes. The lower jaw, which articulates with the skull by the interven- 

 tion of a quadrate bone, is composed of at least two pieces on each side and may 

 contain more elements. The palatines and vomer, and more rarely the parasphenoid, 

 may be armed with teeth, like the upper jaw; but in the frogs and toads the lower 

 jaw is very generally toothless. In all cases the teeth are small, simple, and pointed; 

 being adapted for holding and not for masticating; The shoulder girdle, which is 



largely cartilaginous, is placed 

 very close to the head, and com- 

 prises the usual elements. Each 

 scapula, or shoulder blade, has an 

 upper cartilaginous portion ex- 

 tending inward nearly to the 

 middle line of the back; while in 

 the frogs each metacoracoid has 

 an inward cartilaginous expan- 

 sion, which may either meet or 

 overlap its fellow, and is of much 

 importance in classification. In 

 advance of the metacoracoids is 

 another pair of transverse bars 

 commonly known as the precora- 

 coids; while in front of these is 

 a single median rod termed the 



omosternum; the proper sternum, or breastbone, occupying a similar position 

 behind the metacoracoids. In the fore-limb the radius and ulna may be united, 

 and the wrist cartilaginous; the number of toes among living forms never ex- 

 ceeding four, and being sometimes reduced to three. More variation exists in the 

 hind-foot, the number of toes in the long-tailed forms ranging from two to four, 

 whereas in the frogs and toads it is always five. Only in a few frogs and newts 

 are the toes furnished with claw-like nails; in the greater number of forms these 

 being naked, although often connected by webs, and sometimes carrying adhesive 

 discs on the lower surface. 



In all Amphibians the brain is of a very low type, its component 

 portions lying in a line one behind the other, without overlapping. 

 All possess the three chief organs of sense, although in some instances the eyes may 

 be very minute and covered with an opaque skin. In frogs and toads the eye is 

 large and very highly developed; generally possessing two lids of which the lower 

 one is larger and thinner than the upper, and more or less transparent. Greater 

 variation exists in the structure of the ear, which is simplest in the tailed forms. 

 The nose opens externally in a pair of nostrils situated near the muzzle, and by 

 another pair of apertures into the mouth; the latter characteristic distinguishing 

 Amphibians from the majority of Fishes. The tongue, which acts only in the very 

 slightest degree as an organ of taste, and is wanting in one group of frogs, is gen- 

 erally well developed and thick, filling the whole space between the jaws, and being 



SKELETON OF FROG. 



Soft Parts 



