546 PEOF. T. "W. BEIDGE ON THE MESIAI, 



first radial element (r.e.^) consists only of a bony proximal segment 

 which has the usual dagger-like shape, and, in addition to being 

 slightly expanded, is tipped with a pad of cartilage at its distal 

 extremity. In the second (r.e.^) the cartilaginous distal portion of 

 the segment becomes slightly elongated upwards and backwards, 

 and a distal segment is added. In the third and succeeding 

 elements as far as the seventeenth, the distal cartilaginous 

 epiphyses of the proximal segments (p.s.) gradually assume 

 the proportions and relations of true mesial segments. In the 

 sixth element (r.e.^) an ossific centre makes its appearance 

 in the epiphyses, and, gradually enlarging in the succeeding 

 elements, becomes in the eighth to the twelfth inclusive {r.e/— 

 r.e.^^) a fairly well-developed, hour-glass-shaped mesial segment 

 (m.s.). From the twelfth to the fifteenth the ossified mesial 

 segment becomes gradually smaller and finally disappears. Pos- 

 terior to the seventeenth element the cartilaginous epiphyses of 

 the remaining proximal segments fuse into a continuous strip of 

 cartilage supporting dorsally the corresponding distal segments. 

 All the radial elements, except the first, possess distal segments 

 (J.S.), which from the fourth to the fifteenth are more or less 

 completely ossified, but remain simple cartilaginous nodules in 

 front of the fourth and posterior to the fifteenth. The relations 

 of the distal segments to the mesial segments, and to the proximal 

 segments of contiguous elements, are precisely the same as in 

 Osteoglossum. 



It is obvious, therefore, that the central radial elements of the 

 dorsal fin oiEsox — that is from the sixth to the fifteenth inclusive — 

 are typically trisegmental, and that anterior and posterior to 

 these the elements become bisegmental or unisegmental accord- 

 ing as a distal segment is, or is not, present. 



All the proximal segments, except those pertaining to the first 

 two and the last five radial elements, have each of their lateral 

 surfaces traversed by a more or less well-marked longitudinal 

 ridge, which separates the elevator and depressor muscles of each 

 fin-ray and serves for the partial origin of both. 



Of the twenty-one fin-rays the third, like those succeeding it, 

 is supported by the distal segment of its proper radial element 

 (viz., the third), which is, as it were, clipped by the cleft base 

 of the ray. The two anterior rays simply rest basally on the 

 thickened cartilaginous extremities of the proximal segments of 

 the first and second radial elements. 



