11 PRACTICAL DIRECTIONS 33 



I per cent, in the water, or mix it with about one-third of its l)ulk of 

 methylated spirit, in order to prevent the excessive sweUing of the 

 oviducts. If, however, you wish to make out the blood-vessels in this 

 specimen without injecting them, it is as well to defer putting water 

 into the dish until a later stage of the dissection. 

 Note— 



1. The peritoneum-parietal and visceral layers. 



2. The pericardiitin, containing the heart. If not already opened, 

 the pericardium should be slit through, so that the auricles and ventricles 

 can be plainly seen. If the frog has been killed quite recently, you will 

 be able to observe \ht pulsation of the heart. 



3. The right and left lobes of the liver, and the gall-bladder. 



4. The two lungs: if contracted, inflate with a blowpipe through the 

 glottis. 



5. The enteric or alimentary canal, consisting o{ gullet or cesophagus, 

 stomach, small intestine {duodenum and ileum), and large intestine or 

 rectum communicating with the cloaca, which will be seen at a later 

 stage, and which opens to the exterior by the vent. 



6. The mesentery. 



7. Th^ pancreas. 



8. The spleen. 



9. The uri7iary bladder. If collapsed, insert a blowpipe into the 

 vent and inflate. (You will very likely find some small parasitic flat- 

 worms, called Polystomiim integerrinum, in the bladder ; each worm 

 has a ring of suckers round the hinder end. ) 



10. In the male the spermaries and fat-bodies, and in the female the 

 ovaries, fat-bodies, and oviducts. 



11. ThQ I'idneys a.nd ureters. 



12. The mode of suspension of all these organs (p. 26), and the 

 position of the sub-vertebral lymph-sinus. In order to clearly understand 

 the relations of these parts, a thick transverse section should be made 

 through another frog in the region of the kidneys and examined under 

 water (compare P'ig. 5). 



Sketch the contents of the abdomen in situ. 



The Neural Cavity and its Contents— Now turn the frog with 



its back upwards, and pin it firmly to the bottom of the dissecting-dish 

 or to the dissecting-board as before. Pinch up the skin, make a 

 longitudinal cut through it from the snout to « ithin a short distance of 

 the vent, and turn the flaps right and left. The muscles of the back 

 Pract. Zool. 1-> 



