of the Fishery Board for Scotland. 



269 



so in the adult as to look like scarcely more than half a vertebra. It is 

 provided with a neural arch, forming a smaller aperture than usual; and the 

 short sides of this arch expand into a spine formed of a thin (laterally com- 

 pressed) lamina of bone, which is much shorter than the previous neural 

 spines. Arising from near the median lateral part of the vertebra, and on 

 each side of it, is a strong backwardly and upwardly projecting paired bone. 

 These are closely approximated, but do not fuse together to form a com- 

 plete arch, and the spinal cord lies dorsal to their basal portion, but towards 

 their termination it passes in between them, and they cover and partly 

 overlap laterally the semi-aborted vertebrae of the upturned part of the 

 column. Sometimes the thin flat neural spine of this vertebra is found 

 fused to these bones, which arise so closely behind it, or rather alongside 

 it, as to leave practically no interval between them ; in other cases, again, 

 they can be separated. It would seem as if both of these represented the 

 single neural arch of this vertebra, and the position of the previous two 

 spines, with the strong bar given off at the posterior part of their bases, 

 which forms a second connection with the vertebra, seems to indicate a 

 similar condition. Their appearance in the young herring clearly shows 

 that these are not direct notochordal ossifications. Closely applied to the 

 terminal sharp-pointed portion of these bones, and appearing like splints 

 from it, are three other short bones (two dorsal, one ventral), sharp 

 pointed at their proximal (anterior) ends, and which carry small, partly 

 developed, fin rays covering the dorsal root of the main caudal fin. It 

 is difficult to say whether these entirely represent a single neural spine, 

 or rather, as I incline to think, are an aggregation of the neurapophyses 

 of these last upturned vertebrae.* 



The haemal arch of the terminal vertebra (57th) arises from the body of 

 the vertebra in a rather more lateral position than do the previous arches. 

 Not thickened so much at its tip as those of the 55th and 56th verte- 

 brae, it still forms a fairly large arch, and it is expanded on its ventral 

 edge into a thin lamina (as with the 56th) extending from its base to 

 fully two- thirds of its length. It has however, in addition, on each side, 

 a strong, short, laterally expanded portion at its base, the outer edge of 

 which is continued backwards as a projecting process 2 or 3 mm. in length, 

 which gives attachment to certain of the caudal fin muscles. 



The whole remainder of the base of the caudal fin is composed of five 

 completely ossified, or partly cartilaginous hypural pieces, the proximal 

 portions of which appear to articulate with the bony mass of terminal 

 vertebrae (they are seen to do so in the young fish, where this part is 

 seen as distinct vertebrae). Examination of favourable adult examples, 

 but especially of herring fry, seem to me to indicate clearly that these 

 bones are partly true haemapophyses arising from the upturned vertebrae, 

 and partly ossified connective tissue between them, and that they are 

 not wholly interspinous bones. Closely applied to the dorsal edge of the 

 haemal spine of 57th vertebra, is a wedge-shaped laterally compressed 

 hypural. Its wide end forms its distal extremity, while its narrow 

 proximal end is applied to the (in the adult) scarcely discernible 58th (?) 

 vertebra. It is to be noted, however, that the ventral portion of this bone 

 is flatter than its dorsal edge, and this dorsal edge arises as a somewhat 

 enlarged base. A similarly shaped bone, though rather smaller in lateral 

 area, holds a somewhat similar position dorsal to the central longitudinal 

 line of the fish, as does the other ventral to it, and it appears in part of its 

 substance to represent the haemapophyses of the 59th vertebra. More or 

 less of the expanded portion of these bones appears to be ossification arising 

 from deposit in the intervening connective tissue. In the fry they are 

 * They appear to be the displaced epurals of Ryder. 



