112 PATTEN AND REDENBAUGH. [Vol. XVI. 



tend to draw the endocranium out of place. They may also 

 serve to compress the cephalothorax and thus aid in the expul- 

 sion of the genital products. 



A few muscle strands, plastro-buccal muscles, go from the 

 anterior neural side of the plastron to the oesophagus, and a few 

 more, beneath the skin behind the mouth, go from the occipital 

 ring to the oesophagus. 



A mass of longitudinal abdominal muscles (Text-figs. 5 and 6 ; 

 Pis. VI and VIII, Figs, i and 4, l.a.m.) arises from the posterior 

 haemal side of the endocranium and passes backward, giving off 

 slips to each pair of abdominal entapophyses and to the abdom- 

 inal endochondrites. It terminates upon the integument just 

 posterior to the last pair of gills. Portions of this mass join 

 together the successive endochondrites. A pair of slips are 

 inserted upon the integument posterior to each of the four gills 

 and just median to the infoldings of the tendinous stigmata. 

 They unite with the terminal portion of the mass of abdominal 

 muscles, pass backward, and are attached to the integument 

 posterior to the last pair of gills. 



Four inter-entapophy sial mviSclQS (PI. VIII, Fig. 4, i.e.m.) pass 

 from the first pair of entapophyses to the next four pairs. 



The tendinous stigmata {t.s.^''^) of the six pairs of abdomi- 

 nal appendages furnish attachment for a bundle of brancJiio- 

 l/ioracic muscles (Text-figs. 5 and 6; Pis. VI and IX, Figs, i, 5, 

 and 6, b.t.m) which run forward just neural and median to the 

 row of entapophyses, and external to the large bundle of abdomi- 

 nal muscles proceeding from the endocranium. After passing 

 median to the tergo-coxal muscles, external to the tergo-plastrals, 

 and haemal to the plastro-coxals, the branchio-thoracic muscles 

 attach themselves by two slips (PI. IX, Fig. 5, b.t.m.''^'^^^) to 

 the haemal side of the carapace, external to the pericardial 

 sinus ip.s.). 



Between the branchio-thoracic muscles and the longitudinal 

 abdominal muscles is a double membrane closely investing 

 these muscles like a perimysium, and affording attachment for 

 the veno-pericardiac muscles (see PI. IX, Fig. 6, v.p.mP). 



All of these longitudinal muscles act together as flexors of 

 the abdomen. 



