l6o PATTEN AND REDENBAUGH. [Vol. XVI. 



vate the body portion of the metamere. The haemal nerve is 

 divisible into intestinal {i.n)j, cardiac {s.c.n.), and integumen- 

 tary branches {in.n.), and of these the intestinal and cardiac 

 branches communicate with corresponding branches of other 

 neuromeres by longitudinal connectives. 



(i) Neural or Gill Nerves. — The neural nerve (Text-figs. 

 1 6 and 17, n.n.^) enters the base of the gill and immediately 

 divides into three branches, the external {e.b.n.), median {m.bji.), 

 and internal {i.b.n.) branchial nerves. 



The external branchial nerve gives a motor branch to the 

 abductor muscles {ab.w-fi) of the anterior face of the gill and 

 a sensory branch to the epidermis of the same region and to 

 the outer portion of the base of the gill. 



The median branchial nerve {m.bjt.) gives a motor branch to 

 the external branchial or abductor muscle (e.b.mP) upon the 

 posterior face of the appendage, and a sensory branch {g.n) to 

 the gill book (Text-fig. 17, g.b.). This passes outward posterior 

 to the branchial cartilage {b.cP) to the inner edge of the gill 

 book, where it divides into two bundles of fibers which go in 

 opposite directions along the edge of the gill book, and give off 

 a fine nerve fiber to each gill leaf. These fibers follow the 

 margins of the leaves and break up into fine filaments which 

 supply the numerous sense buds in the epidermis. 



The internal branchial nerve supplies the muscles {p.l.m. and 

 i.l.m.) and epidermis of the distal portions [o.l. and i.l.) of the 

 appendage, and corresponds very closely to the third branch 

 {i.o.n.) in the operculum. The median lobe {in. I.) of the ap- 

 pendage is also supplied by a branch from the internal branchial 

 nerve. 



(2) Haemal Nerves. — The haemal nerve (Text-fig. 16; Pis. 

 VI and VIII, Figs, i and 3, h.n.'^'^) of the branchial neuromere 

 arises from the anterior end of the abdominal ganglion and 

 passes out over the neural surfaces of the longitudinal abdomi- 

 nal muscles, anterior to the appendage of its own metamere. 

 It divides into three principal branches — {a) intestinal, {b) 

 cardiac, {c) integumentary branches. 



(a) Intestinal Branches. — In all the gill neuromeres the intes- 

 tinal branch {i.n.'^'^) arises from the proximal end of the haemal 



