1 6 ELEMENTARY BIOLOGY. [CHAP. 



latter. On the dorsal aspect the large intestine presents a 

 slight forward dilatation, which may be regarded as a rudi- 

 ment of a caecum. 



The liver is very large, and incompletely divided into 

 two lobes, the left of which is further subdivided into two. 

 The gall bladder is attached to the posterior face of 

 the right lobe. The bile duct opens into the duo- 

 denum, at some distance behind the pylorus, running 

 through the pancreas and receiving the duct of that organ 

 on its way. 



The rounded spleen lies in the mesentery, projecting 

 more to the left than to the right side, near the point at 

 which the small intestine first becomes coiled. 



The apparatus of circulation in the Frog consists of the 

 blood and lymph vessels and their contents. 



The lymph is a colourless fluid containing colourless 

 nucleated corpuscles which exhibit amoeboid movements: 

 it is contained partly in large spaces immediately beneath 

 the integument; in the pleuroperitoneal cavity and pro- 

 bably in the other serous cavities; and, partly, in capillaries 

 and larger trunks which are interlaced with and accompany 

 the blood-vessels. The largest of the trunks is the great 

 sub-vertebral lymph-sinus, which lies between the layers of 

 the root of the mesentery and communicates by small pores 

 with the pleuroperitoneal cavity. 



The blood consists of a colourless plasma which contains 

 colourless corpuscles, similar to those of the lymph, and in 

 addition a great number of oval nucleated red corpuscles. 

 It is contained in the blood-vessels, which consist of capil- 

 laries, arteries and veins, the two latter being connected on 

 the one side by the capillaries and, on the other, by the 

 heart into which they open. The lymphatics and the 

 blood-vessels are brought into connexion with one another 



