Report of the* State Geologist. 



501 



Thus, in the pedicle- valve of any living brachiopod likeTKREuRA- 

 tulina or Magellania, the principal diductor or opening muscles 

 take their origin at the anterior edge of the visceral area and on 

 either side of the axial line. They rapidly diminish in size in 



Fig. 113— Muscular system of 

 Magellania. a, adductors; 

 d, d, diductors; c, cardinal 

 process; s, septum of 

 brachial valve; 6, brachial 

 supports. (Davidson). 



Fig. 114. — Magellania flavescens. a, pedicle- valve; 6, 

 brachial valve; c, adductor scars; d, diductors; e, acces- 

 sory diductors; p, ventral pedicle-muscle; v, median 

 pedicle-muscle. (Davidson.) 



crossing the interior cavity, and their small extremities are 

 inserted on the anterior portion of the cardinal process of the 

 brachial valve. These muscles are, almost without exception, the 

 largest, and leave the deepest scars upon the shell of any in the 



Fig. 115.— Hemithyris psittacea. a, pedicle-valve; b, brachial valve; c, posterior adductors; 

 d, anterior adductors; e, diductors; /, pedicle-muscles. (Davidson.) 



animal. The reason of this is that the muscles by contraction 

 act upon a very short lever-arm (cardinal process) through which 

 they must overcome the resistance expressed in the weight of the 

 entire body of the brachial valve attached by its posterior 



