31 



cutting edge of the Jaw. This edg>' is drawn up into a strong median tooth 

 which is tlanked !)>• a jiaii' of small notches. The pharyngeal muscles are attach- 

 ed to the adjacent surfaces of the lamellae of each jaw and fill the narrow 

 space between them. The jaws grow constantly by additions to their margins 

 and to their unexposed surfaces. They ai'e marked by two sets of fine 

 striae , the lines of growth , one set concentric with the point of the ydw and 

 one set radiating from it. The jaws are brown- 

 ish-black on the cutting edges, amber colored 

 near those edges, and colorless at the fiee 

 margins. 



The upper mandible is almost as long as 

 the pharynx and is shaped like the prow of a 

 very deep and narrow boat. Its inner lamella, 

 to the dorsal end of which the oesophagus is 

 attached , forms the greater portion of the lining 

 of the oral cavit>'. The outer lamella is more 

 strongly curved and is not half as large as the 

 inner. The levator mancHbidi is attached to its 

 dorsal end. 



The lower mandible is about half as long as 

 the upper but is less compressed and more 

 curved so that it fits over the distal end of the 

 inner mandil^le. The inner lamella has much 

 the same shape and size as the outer lamella of 

 the upper jaw ; the outer lamella of this jaw , 

 is a long, broad band which extends backw^ard 

 parallel to the edge of the jaw and forms a 

 pair of prominent wings, the alae. The upper 

 jaw is comparatively fixed while the lower rotates 

 thru an angle of 45° about an axis which passes 

 almost thru the middle of each side of the 

 inner lamella of the upper jaw. The muscular 

 fibres (Text figure 11. c) which move the jaws arise from the inner lamella 

 of the upper jaw and take a spiral course around this axis. The fibres (3 in 

 the figure) from the lower portion of the middle of the innei lamella of the 

 upper jaw pass directly outward and are inserted in a strong, superficial fascia 

 which is attached to the outer lamella of the lower jaw and which covers 

 the lower half of the pharynx. These fibres form a central column around which 



