THE FROG, OR THE TOAD. Ill 



Exercise 3. Sketchy in the natural position, the internal organs thus ex- 

 posed, including the outlines of the entire body. 



Exercise 4. Draw a small bundle of muscular tissue and a single fiber of 

 the same as seen under the microscope. 



INTERNAL ANATOMY. The following notes will serve as a guide in 

 locating and identifying the various internal organs; as the animal is 

 lying on its back the student will bear in mind the reversal of the cardi- 

 nal directions, "right" and "left:" 



a) In the front part of the body cavity is the heart, still pulsating if you 

 are using a fresh specimen. Time the pulsations for several minutes 

 and see if they are regular. Remove the thin pericardium that 

 envelops the heart. The lower, pointed part of the latter is the 

 thick walled ventricle; the pulsating pockets at the top are the 

 right and left auricles. Raise the point of the heart and watch 

 the order of contraction. Near the top of the organ, and to the 

 right of the center, is the conus arteriosus from which arise two 

 large arteries. Follow these until you find each dividing into 

 three branches an upper, carotid artery going to the region of 

 the head, a lower, pulmonary artery carrying the blood to the 

 lungs and skin, and, between the two, the large systemic artery. 

 The impure blood from the returning veins is poured into the 

 right auricle, the pure blood from the lungs and skin into the 

 left auricle. Both auricles discharge into the single ventricle, 

 from which the mixed blood is sent out as indicated above in the 

 discussion of the conus arteriosus. 



b) Flanking the heart on each side and extending below it is the liver. 



How many lobes has it ? Note the gall bladder attached between 

 the two main lobes on the under side. If possible trace its con- 

 nection, by means of a bile duct, with the alimentary canal. 



c) To the left of the liver is the stomach, communicating with the 



back part of the mouth cavity pharynx through the oesopha- 

 gus. 



d) Trace the small intestine from the stomach to the rectum, an 



enlarged division of the tract near the anal end. The portion of 



