THE FROG . 203 



With the organs all in position, now make out the rectum; the bladder; 

 the spleen; the cloacal chamber; the kidneys; the spermaries; the ovaries 

 and oviduct in the female, and the spermaries and vas deferens in the male. 



Remove the heart, liver, stomach, and intestines. This will disclose 

 the lungs; the two systemic arteries uniting to form the dorsal aorta, 

 which should be traced to where it divides to supply the legs; the nerves 

 to the arms; nerves to the back; three large nerves arising from the back- 

 bone and extending toward the legs, and finally uniting to form the sciatic 

 plexus, from which arise the large nerves entering the leg. By lifting up 

 the aorta gently, delicate branches of the sympathetic system may be 

 seen and traced to their ganglia. 



One leg of the animal should be dissected to make out the muscles, 

 nerves, bones, and joints. The muscles should be separated from each 

 other and traced to their origin and insertion, special notice being taken 

 of the long tendons extending from the lower muscles down to the toes. 

 In the joints, note the freedom of motion of the bones; the tendons, which 

 extend over them; the rather loose ligaments that unite the bones; the 

 readiness with which the bones come apart when the ligaments are cut; 

 the smooth surfaces of the ends of the bones; and the cartilage that covers 

 their ends. (If there is time for more careful dissection, reference must be 

 made to laboratory guides on the dissection of the frog.) Clean all of the 

 soft parts from the bones of the leg, separating and identifying each bone. 



Examine the eyelids; the iris; the pupil. Make an incision through 

 the iris and remove the lens; note the cavity of the eye behind the lens. 

 Cut an incision through the tympanic membrane, noting the shallow 

 cavity beneath it, the tympanic cavity, the bony columella extending 

 across it to the skull. A bristle thrust into the bottom of this cavity will 

 enter the mouth through the eustachian tube. 



Remove with a knife a bit of the flat bone on top of the skull, exposing 

 the brain; and then, with forceps and scissors, break away the bone so 

 as to expose completely the brain and spinal cord down the back to the 

 urostyle, taking care not to injure the soft parts. Identify all parts of 

 the brain as described on page 193. 



The skeleton should be studied from another specimen. Remove all 

 the soft parts from the skeleton, separating all the bones. Clean and iden- 

 tify each (Fig. 88), and compare with the mounted skeleton. 



BOOKS FOR REFERENCE 



ECKER, The Anatomy of the Frog, The Macmillan Co., New York. 

 HOLMES, Biology of the Frog, The Macmillan Co., New York. 

 MARSHALL, The Frog, The Macmillan Co., New York. 

 MORGAN, Development of Frogs' Eggs, The Macmillan Co., New York. 

 GUYER, Animal Micrology, University of Chicago Press, Chicago. 



