20 THE FROG chap. 



which will be seen in the course of the 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 

 f<5rin 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 co:/oiiu\ 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- 

 fire 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 auricles. 

 'i'he heart is enclosed in a transparent, membranous bag, 

 the pericardium (pcd). 



Just behind or posterior to the heart are two 

 large masses {Ir), usually of a dark reddish-brown 

 colour ; these are the right and left lobes of the liver. 

 'J'hey extend forwards, one on each side of the heart : 

 between them is a globular bag of a greenish colour (Fig. 3, 



