448 



THE SENSORIAL FUNCTIONS. 



the sclerotica : its fibres descending in a parallel 

 course towards the optic nerve, where they termi- 

 nate, by a semi-circular edge, in a tubular tendon. 



This tendon has no particular attachment, but is 

 employed for the purpose of serving as a loop for 

 the passage of the long tendon of the second 

 muscle (p), which is called the pyramidalis, and 

 which arises from the lower and back part of the 

 sclerotica. Its tendon (t), after passing through the 

 channel above described, which has the effect of a 

 pulley, is conducted through a circular sheath, 

 furnished by the sclerotica to the under part of the 

 eye, and is inserted into the lower portion of the 

 loose edge of the nictitating membrane. By the 

 united action of these two muscles, the former of 

 which serves merely to guide the tendon of the 

 latter, and increase the velocity of its action, the 

 membrane is rapidly drawn over the front of the 

 globe. Its return to its former position is effected 

 simply by its own elasticity, which is sufficient to 

 bring it back to the inner corner of the eye. If 

 the membrane itself had been furnished with mus- 

 cular fibres for effecting this motion, they would have 



