XIII.] THE FROG. 189 



floor of the mouth and to the front part of the lower 

 jaw. Notice the slit of the glottis in the hinder 

 part of the floor of the mouth, and above this the 

 opening of the oesophagus. Pass a bristle into the 

 former, and a probe into the latter. Notice the 

 fine teeth in the upper jaw and on the palate. 



b. The trunk. 



Tapering towards the hinder end; and allowing 

 the hard parts of the skeleton to be felt beneath 

 the soft integument on the dorsal side, and in the 

 anterior half of the ventral aspect ; rounded and 

 soft on the greater part of the sides and belly ; 

 the doacal aperture near the dorsal surface of the 

 posterior end of the trunk. 



c. The limbs. 



a. The anterior pair; their three subdivisions, 

 brachium, antebraohium, and manus ; the four 

 digits. 



/3. The posterior pair; their length as compared 



with that of the anterior ; their subdivision into 



femur, crus, and pes : the five long digits; 



the well-developed web ; the horny prominence 



(see p. 154). 



3. Kaise the integument of the abdomen with forceps 

 and slit it open with scissors from the lower jaw to 

 the origin of the hind limbs, a little on one side of 

 the middle line. Observe the spacious lymph cavities 

 between the skin and the subjacent muscular wall of 

 the abdomen ; also a vein which occupies the middle 

 line of the inner face of this wall and is usually 

 visible through it. 



