CHORDATA. 319 



The heart: Does this organ lie free in the body cavity? 

 What is the shape of the heart? To what is it attached? 

 Identify the auricles in front, and the ventricle behind. Can 

 you recognize the aorta arising from the ventricle; and the 

 venous sinus dorsal to the heart and receiving the large veins? 

 How many chambers to the heart ? Their relation to each 

 other ? 



Further study can be pursued successfully only by injecting 

 the vessels with a colored mass. 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.) 



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. What is their posi- 

 tion in relation to the vertebrae? How many pairs can yon 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. 



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. 



