244 ELEMENTS OF MAMMALIAN ANATOMY 



8. Which spinal nerves form the several plexuses? 



g. Make a ilrawing showinj; wherein the brachial plexus in your specimen 

 differs from that described in the text. 



10. Write a description of your dissection of the nerves of the thoracic limb, 



11. Mention in what way the lumbar plexus dilTers from the description 

 in the book. 



12. Draw the great sciatic nerve and its branches as seen from the caudal 

 aspect. 



13. What nerves supply the digits? 



14. Describe the chief plexuses of the sympathetic system. 



15. How do stimuli from the viscera reach the brain? 



16. What portion of the body is not supplied with nerves from the sympa- 

 thetic system? 



THE ORGANS OF SENSE 



The organs of sense are the specialized peripheral termina- 

 tions of the sensory nerves, and are so constructed as to be 

 capable of receiving only a certain kind of stimulus. The 

 stimuli for the eye are ether vibrations; those for the ear are 

 vibrations of the air. The stimulation of the sensory nerves 

 produces sensations in the cells of the cerebral cortex to which 

 they lead. 



The external stimuli giving rise to the internal sensations 

 of seeing, hearing, smelling, and tasting are transmitted by 

 only four pairs of cranial nerves, while the stimuli of cutaneous 

 sensations are transmitted by three pairs of cranial nerves 

 and all the spinal nerves. 



Cutaneous Sense Organs. — The cutaneous sense organs are 

 composed of the endings of the sensory nerves in all parts of 

 the skin and the mucous membrane of the mouth, nose, 

 arms, vagina, and urethra. One kind of sense organs, those of 

 pain, are present in every organ of the body. The sense organ 

 of pain is probably an unmodified free nerve-ending. 



While all portions of the skin and perhaps other parts of the 

 body are supplied with organs capable of receiving stimuli 

 giving rise to tactile sensation, the soles of the feet and the 

 skin at the base of the vibrissae are specially sensitive regions. 



