500 



Forty-fifth Report on the State Museum. 



contraction open the valves (diductors), those which by contrac- 

 tion close the valves (adductors), and those which by contraction 

 withdraw the pedicle (pedicle-muscles). The arrangement of 

 these is uniformly simple, and the plan is not essentially varied 



HFig. 110.— Lingula Murphiana. (Davidson.) 



Fig. 111.— Extremity o 

 pedicle of Lingula ana 

 Una, with horny sheath 

 laid open, exposing the 

 muscular cylinder and 

 its membraneous coat. 

 (Hancock.) 





Fig. 112.— Transverse 

 section of pedicle of 

 /. i)i g u 1 a a ii at i h a. 

 (Hancock.) 



throughout the articulate group. As to the valvular muscles, it 

 js a noteworthy fact that the same muscular action (contraction) 

 produces directly opposite results, on account of the difference 

 in the position of insertion of the muscles of the brachial valve. 



52 



