106 EXPERIMENTAL PHYSIOLOGY 



string vibrate faster or slower than a long one? What effect 

 has rate of vibration on the pitch of a sound? 



C Strike the wire gently. Note the distance at which 

 the sound can be heard. Strike harder. Is the tone louder 

 or softer? Can it be heard at a farther distance? Does it 

 vary in pitch? What effect on sound does extent (amph- 

 tude) of vibration have? 



D. Stand at the point where you can just hear the tick- 

 ing of a watch. Now make a conical tube of paper and 

 insert the small end in the ear. Point the large end toward 

 the watch. Can you hear it any better now? What part 

 of the ear serves a purpose similar to that of the tube? 



LXX. — ^Vision; Dissection of Sheep's Eye. 



Apparatus. — Sheep ^s skull with eyes in socket (the skull used 

 in Ex. LXIII will serve for this purpose), scalpel, scissors, bone 

 forceps, evaporating dish. 



Directions. — Cut away, with the bone forceps, the bones 

 that inclose the eye, so that it may be seen in position from 

 the side. 



A, Muscles. Notice that the motion of the eyeball is con- 

 trolled by six muscular bands. Locate the attachment of 

 four of these bands on the top {superior rectus) , bottom 

 {inferior rectus), side near nose {internal rectus), and side 

 farthest from nose {external rectus). Note that these ex- 

 tend directly backward to the end of the socket and have 

 their origin there. What motions do these muscles give to 

 the eyeball? Now locate on the top of the eyeball the at- 

 tachment of a transverse band of muscle (the superior ob- 

 lique) and follow its course, through a tendon pulley, to 

 its origin at the back of the socket. In what direction 



