98 THE FROG CHAP. 



and just behind the transverse process of the third 

 vertebra : the posterior pair (p. ly. ht) are situated one 

 on each side of the posterior end of the urostyle. These 

 organs pulsate regularly, like miniature hearts, and 

 pump the lymph into the veins, the anterior pair com- 

 municating with the subclavian, the posterior with 

 the renal portal vein. 



The lymphatics of the enteric canal have an important 

 function to perform in that they absorb the fatty portions 

 of the food (p. 75). The fluid they contain has a milky 

 appearance, owing to the presence of minute suspended fat- 

 globules, and for this reason they receive the name of 

 lacteals. 



The coelome is really a great lymph-sinus (Fig. 23, 

 ccel). It communicates with the veins of the kidneys 

 through certain microscopic apertures called nephro- 

 stomes (nst). 



The spleen (p. 23, and Fig. 3, spl) has important 

 relations with the blood- and lymph- vessels, and probably 

 acts as a blood-filter, removing particles in the blood 

 which are no longer wanted. 



PRACTICAL DIRECTIONS 



The Vascular System. 



a. Let some blood from a frog or better from the veins 

 of some larger, freshly-killed, warm-blooded animal, such 

 as a rat or a rabbit flow directly into a white cup or porce- 

 lain capsule. Note that it soon coagulates, and shortly 

 afterwards separates into clot and serum. Notice also the 

 difference in colour between the blood freshly drawn from 

 a vein (see p. 85), and that soon assumed by exposed portions 

 of the clot. 



b. Pin a freshly-killed frog to the dissecting-board, dorsal 

 side upwards, and cut through the skin of the back along the 

 urostyle. The posterior lymph-hearts (p. 98, Fig. 23) will 

 then be seen. To make out the anterior lymph-hearts, care- 

 fully separate the supra-scapulae from the vertebral column. 

 Some of the chief lymph-sinuses have already been seen : 

 special methods are required to trace the lymph-vessels. 



