78 MINUTE STRUCTURE OF THE BRAIN AND CORD OF ARACHNIDS. 



The Haemal Nerve Roots. — The hsemal nerves arise from the anterior haemal 

 margin of the neuromere and extend upward and outward. In the more pos- 

 terior segments, their apparent point of attachment shifts forwards to a point 

 midway between the two neuromeres, but without changing the root terminals. 

 (Fig. 59.) They contain the following fascicles : 



a. A bundle of large motor fibers arising from the D neurones on the neural 

 surface of the opposite side, in the next anterior neuromere. (Figs. 61, 62. h.r^.) 

 It runs along the haemo-lateral margin of the cord, becoming more and more dis- 

 tinct as it approaches the next following neuromere. There it bends outward 

 onto the anterior haemal surface of the haemal nerve, dividing into two fascicles. 

 One forms the small, purely motor nerve supplying the haemo-neural and the 

 longitudinal abdominal muscles, l.ah.; the other passes into the main part of the 

 nerve, and separates farther on, as the branch that supplies the branchio-thoracic 

 muscles. (Fig. 59, b.th.) (hypoglossal elements.) 



b. A large fascicle of pale fibers (Figs. 61 and 62, H.r'), that extends along 

 the anterior neural margin of the nerve. On entering the cord, it runs diagonally 

 forward, inward, and upward, terminating in an elongated mass of neuropile, 

 on the median, neural surface of the next anterior neuromere. Its peripheral 

 termination is unknown. Probably cardiac. 



c. A large central fascicle, H.r^, terminates in a conspicuous, isolated mass of 

 neuropile of the same side, near the anterior median region of the same neuromere. 

 Some of the fibers pass through the neuropile, neurad, and cephalad, joining the 

 median, longitudinal, neural tracts. Probably general cutaneous fibers. 



d. This fascicle, H.r^, is not easily followed in sections, but its fibers are 

 frequently seen in methylene blue preparations. They spring from the large 

 neurones A, on the opposite side of the neuromere. Their collaterals are shown 

 at a'. (Figs. 61, 62.) 



e. This fascicle extends backward toward the neuropile center of the bran- 

 chial nerve, H.r^. (Fig. 61.) 



/. The intestinal fascicle is a small bundle of fine fibers, int. In the anterior 

 segments, it leaves the cord with the haemal nerve; in the more posterior ones, it 

 arises separately. (Fig. 59, F""^.) In the first ganglion (Fig. 61, int.), it runs 

 along the posterior side of the haemal nerve and then turns sharply forward over 

 the neural surface of the sensory root, H.r^, to a small, ill defined group of cells 

 lying in group A. 



We find, therefore, in the haemal nerves, the following roots or fascicles : two 

 sensory roots terminating in neuropile on the neural surface of the cord, on the 

 same side, one in the same neuromere, H.r'\ the other in the one next in front 

 of it, H.r^. (Fig. 60.) Two roots, ending in cell groups on the opposite side of the 

 cord, one group, D, on the posterior neural side of the next anterior neuromere, the 

 other, on the anterior neural surface of the same neuromere, 4. A fifth root, 

 H.r^, extends caudad, disappearing in the neuropile near the base of the neural 

 nerve. The intestinal branch should perhaps be counted as a separate nerve. 



