27 



From the margin of the oral face of the capsule arise 

 five interradiallj^ situated and diverging pairs of cord-like 

 extensions of the capsule (PL V., figs. 48 and 49). Trend- 

 ing towards the oral face of the disc, and entering the 

 substance of the radial plates through the apertures seen 

 in fig. 4, PI. I., these cords unite to form five radial 

 nerves, the left cord of one interradial pair uniting with 

 the right one of the pair next to it. Just beyond the 

 points of junction of the cords the five radial nerves are 

 connected together by a pentagonal commissure (PL V., 

 figs. 48 and 49 ; PL YI., fig. 56, 'pnt. com.) lodged in a 

 canal of corresponding shape which traverses the five 

 radials, in the lateral faces of which its openings may be 

 seen (PL I., fig. 6). Beyond the commissure the radial 

 nei'\'e cords pass out of the radial plates into the axial 

 canals of the first primibrachials, and from thence into 

 the second primibrachials or axillaries. On entering the 

 latter each nerve divides into right and left branches 

 (PL VI., fig. 53), which pass outwards through the 

 corresponding oblique facets of the plate to form the axial 

 cords of the arms. The two branches are connected 

 together just beyond their point of origin, and while still 

 within the axillary plate, by a transverse commissure 

 {tr. com.) and a chiasma {chi.), the latter occupying the 

 triangular space bounded by the former and the diverging 

 cords. Passing outwards from the Axillary plate, each 

 branch enters the arm of its own side to become the brachial 

 nerve cord of the apical system [hr. nv. c). Traversing the 

 whole length of the arm through the axial canal which 

 perforates all the calcareous joints, the cord gives off 

 alternately right and left branches to the pinnules, and 

 these arise from double roots (PL YL, fig. 60, cl. r. pn. hr.). 

 Further, the cord gives off in each joint two pairs of 

 nerves (PL III., fig. 29) which are considered to be 



