Materials.
Freshly killed or preserved frogs in dishes or shallow pans of water, forceps, and, if the pupil is to do any dissecting, scissors.
Directions and Observations.
The specimens may have been opened by the teacher, or may be dissected by the pupil as follows:—
Placing the frog on its back, with forceps firmly grasp the skin of the abdomen and the muscles beneath, just in front of the hind legs, and with the scissors cut straight forward in the middle line until the floor of the mouth is reached; this will separate the arms. Care must be taken not to cut too deeply, but this may be avoided by keeping the skin uplifted. Now cut sidewise in front of each hind leg in order that the body wall may be laid aside. Under the arms the heart will be seen; it will be studied as a part of the circulatory system.
Identify the following organs:—
Liver, the large red or brown mass, consisting of several divisions and lying close up under the arms. Bile sac, small, green, and between the liver lobes. Alimentary canal.
- Mouth.
- Esophagus.
- Stomach, the elongated, light-colored, firm, and muscular portion.
- Small intestine, a slender, more or less closely coiled, tubular portion.
- Large intestine, a thin-walled enlargement at the posterior end of the canal.
- Duodenum. This is a muscular portion of the small intestine immediately following the stomach, against which it is folded.
Note.—Specimens secured in late fall, winter, or early spring may contain, if female, a large number of dark-colored eggs; or if male, two white testes, located near the kidneys and similar to them in form, though smaller.