VISCERA OF THE FROG 1 



1. Pin out a freshly chloroformed Frog, with the ventral surface up, in a 

 dissecting tray. With fine forceps lift up the loose skin near the posterior 

 end of the abdomen, and then with scissors make a longitudinal incision, 

 through the skin only, just to one side of the median line and running from 

 the posterior end of the abdomen to the throat region. Make a transverse 

 incision in the skin in the pelvic region, and also one just posterior to the 

 fore limbs. Pin out the flap of skin on each side. 



2. In the same way make a longitudinal cut through the muscle tissue 

 of the body wall, running from the pelvic region to the sternum. Cut 

 through the bony shoulder girdle on each side of the sternum, being 

 careful not to injure the underlying heart. Make transverse cuts as before 

 and pin the flap of body wall on each side over the flap of skin previously 

 pinned out. 



3. Examine the large coelom filled with the viscera, which you have 

 now exposed. It is fined with a delicate membrane (peritoneum) which 

 is continuous over the various organs in the body cavity. The peritoneum 

 also forms folds (mesenteries) by which certain organs are suspended 

 and held in place. Identify and study the following structures : 



(a) The heart, at the anterior end of the coelom, enclosed in a delicate, 

 transparent sac (pericardium). Carefully remove the pericardium. 

 Watch the pulsations of the heart and determine the number per minute. 

 Place your finger tip on the heart while it is beating and note the alternate 

 tension and relaxation. Locate: (i) the single, thick-walled posterior 

 ventricle; (ii) the pair of thin-walled anterior auricles; and (Hi) the 

 conus arteriosus which leads anteriorly from the ventricle. Lift the 

 heart and locate, underneath, the sinus venosus which opens into the 

 right auricle. 



(b) The lungs, consisting of a pair of thin-walled vascular sacs which 

 communicate to the exterior through the glottis in the mouth. The lungs 

 lie close to the dorsal body wall on each side, near the heart. 



(c) The liver, consisting of three large, reddish-brown lobes which lie 

 in a prominent position lateral and posterior to the heart. Separate the 

 lobes slightly and find the gall bladder, which receives bile from each 

 of the lobes. 



iB. pp. 181-184. 

 325 



