20 THE FROG CHAP. 



dissection, are thin- walled tubes full of blood, as will be 

 proved if you should happen to cut one of them, when 

 the blood will escape in considerable quantity. 



Between the right and the left fore-limbs the ventral 

 region of the trunk is protected by certain bones which 

 form part of the shoulder-girdle : projecting backwards 

 from this in the middle line is a flat, heart-shaped plate 

 of a softer, gristle-like substance, known as cartilage 

 (compare Fig. 12). Immediately between the thighs a 

 cartilage called the pubis, part of the hip-girdle (Fig. 14), 

 can be felt. Between the shoulder- and hip-girdles the 

 ventral body-wall is soft, being formed only of muscle 

 and connective-tissue. 



The Abdomen and its Contents. By cutting through 

 the muscles of the belly or abdomen, a large cavity, the 

 body-cavity or ccelome, is exposed, in which are contained 

 numerous structures presently to be described. In order, 

 however, to open the whole of the cavity the ventral 

 part of the shoulder-girdle must be removed. 



In the middle line, between the fore-limbs, and there- 

 fore covered in the entire animal by the shoulder-girdle, 

 is a pink conical body (Figs. 3 and 4, v) connected in 

 front with a thin- walled bag (r. au, I. au), of a purplish 

 colour. The whole thing is the heart : the pink 

 posterior portion is called the ventricle : the purple 

 anterior part consists of two chambers, the uuricles. 

 The heart is enclosed in a transparent, membranous 

 bag, the pericardium (pcd), which contains a lymphatic 

 fluid. 



Just behind or posterior to the heart are two large 

 masses (Ir) which have a dark reddish-brown colour ; 

 these are the right and left lobes of the liver. They 

 extend forwards, one on either side of the heart : between 

 them is a globular bag of a greenish colour (Fig. 3, gl. bl), 

 the gall-bladder. In front of the liver and left and right 



