Characteristics of the Vertehrata. Ixiii 



mentary in this class. Though there is never any prolongation of 

 costal structures to the medio-ventral line^ there is a true sternum 

 developed in relation with the eoracoids in most Amphibia except 

 Caeciliae and Proteus. The ilium never abuts upon more than a 

 single vertebra, but the ilium of one side has been observed to abut 

 upon one, whilst the ilium of the other abutted upon another ver- 

 tebra. No ^parostotic^ bones are ever developed in relation with 

 either limb-girdle. 



In the highest order of Amphibia, the Amira, the tongue is 

 attached to the front of the mouth and is protrusible ; with the 

 exception of Pipa and Bactylethra, where the organ is altogether 

 absent. It is not protrusible in other Amphibia. Amj^hibia are 

 sometimes edentulous ; but usually more or fewer of the bones 

 forming the walls of the mouth, and amongst these, the vomerine, 

 pterj'goid, and sphenoid as well as the lower jaw, the maxillary 

 and the praemaxillary bones, are dentigerous. In Proteus, the 

 digestive canal tahes a direct antero-posterior course, without any 

 specialization of the stomach as a segment of larger calibre than 

 the intestine ; in other Amphibia a small and a large intestine are 

 ordinarily differentiated as well as a stomach. The small intestine 

 of the larvae of the Anura, which, during that period, feed on vege- 

 table food, is of great length and disposed in numerous coils. At 

 the conclusion of their metamorphoses, the digestive tract has as- 

 sumed a comparatively simple character, though the calibre, direc- 

 tion, mucous and muscular coats of the stomach, small intestine, 

 and colon, severally, are most characteristically developed. A bilobed 

 liver and a compact pancreas are always present, but oral salivary 

 glands arc represented only by small glandules impacted in the 

 mucous membrane of the mouth. 



The heart consists of a sinus venosus, a right and left auricle, a 

 single ventricle, and an arterial bulb. Within this latter portion of 

 the organ, a longitudinal lamellar ridge is developed, which is 

 attached along the dorsal line of the bulb and projects freely into 

 its interior ; being connected at either end with a semilunar valve, 

 and describing a curve like that of an italic s, in the interval be- 

 tween those points. This imperfect dissepiment may be held to 

 foreshadow the differentiation of the pulmonary and systemic ar- 

 terial trunks which we find in Ileptiles ; whilst physiologically, by 

 its relation to the orifices of the branches passing to the anterior 



