322 ZOOLOGY 



least a specimen thus injected and dissected by the teacher 

 should be used to demonstrate the three aortic arches (carotid, 

 systemic and pulmonary), the dorsal aorta and its chief branches. 

 5. Muscle. Strip the skin from the leg like a stocking. 

 Without cutting, separate the muscles from each other, demon- 

 strating their general shape and the tendons at the ends by 

 which they are connected with the bones. The end attached 

 to the least movable bone is the origin, the other, the insertion. 

 What is the origin and what the insertion of the large muscles 

 of the thigh? Are the muscle fibres plain or cross-striate ? 

 (Examine a small bit under the microscope after teasing it 

 apart as much as possible.) These studies may very well be 

 extended to include the muscles of the throat, chest, arm, ab- 

 domen, and leg. In all such studies the most important ques- 

 tion the student can ask and answer is this: "What does this 

 muscle do when it contracts?" To answer the question one 

 must find the origin and insertion of the muscle, as well as its 

 relation to other muscles. 



6. Nervous System. Remove with great care the skin, muscles and bone from 

 the roof of the skull so as to expose the brain. Continue backward and expose the 

 anterior portion of the spinal cord. Sketch, as it appears from above, and identify, 

 beginning with the anterior end: 



Olfactory lobes. 



Cerebral hemispheres; number, size, form. Are they separate? 



Optic lobes. 



Cerebellum; a narrow transverse band. 



Medulla oblongata, tapering into the spinal cord. 



Examine the nerves arising from the spinal cord. Look within the body cavity 

 also for these. What is their position in relation to the vertebrae? How many 

 pairs can you discover? Does each arise by a single or double root? Find the 

 large nerve (sciatic) which is the chief nerve of the hind leg. How many spinal 

 nerves enter into the formation of it ? Seek a similar plexus in connection with the 

 front leg. Seek the sympathetic ganglia in body cavity on either side of the 

 backbone. 



Dissect the bone and muscle from one side of the skull, showing the cranial 

 nerves. Begin at the anterior end and identify: (i) the olfactory nerve; cut, and 

 lift the brain slightly, showing (2) optic nerves. Cut these as far from the brain as 

 possible. 



Note other smaller nerves and cut these. How many are there? From what 

 part of the brain do the majority of them arise? Do the optic nerves join at the 

 point where they enter the brain? 



7. Skeleton.- Pick the bulk of the flesh from the bones of an uninjured skeleton. 

 A few minutes of boiling will be of advantage in the final stages of cleaning. 



