of the Fishery Board for Scotland. 



261 



terally triangular than in the young fish, while its edge is slightly irregular 

 in outline. In the first two vertebrae these basal pieces are wanting, and 

 they disappear again at the 24th or 25th vertebra. Along the anterior 

 vertical edge of these basal pieces a more complete ossification takes place. 

 At first it is a bony edge merely, but becomes stronger on the latter ones, 

 and forms a sharp point below (fig. 4, hcem). It is noticeable, however, 

 that if the basal piece is removed from the vertebra, this bony piece which 

 forms the true haemal arch comes with it, i.e., it is not fused to the 

 vertebral body, and this may be the case on the vertebra bearing the last 

 fixed rib, though more or less ossification between the vertebra and this 

 spur may have taken place on the 23rd or 24th, where also the basal 

 piece, as a distinct element, disappears. On the vertebra, however, behind 

 the last fixed rib, the basal piece has almost disappeared, and the bony 

 anterior edge (now become a strong-pointed haemapophysis) is firmly fused 

 with the vertebral body. In the young fish a similar condition of things 

 is to be seen, except that the ossified bar is not so completely developed 

 on the more anterior of these basal pieces (fig. 14, hcem). It appears as 

 a small bony bar not reaching the base or tip of the j.basal piece, but 

 gradually increasing in length backwards until it comes to fuse with the 

 vertebra. In the young fish also the basal piece can be distinguished, 

 although becoming much smaller, as far as about the 30th vertebra. 



In the young fish the hEemapophysis and neurapophysis of each side, 

 together with and connected by a curved bony bar, formed by the gradual 

 extension along the anterior lateral edge of the vertebra immediately behind 

 the terminal thickening, may be completely removed from the vertebral 

 centrum, in which the slightest ossification only at this stage may have 

 occurred (PI. XVI. fig. 13). Ossification proceeds also backwards over 

 the basal piece to form a short sharp-pointed downwardly and back- 

 wardly projecting process. From examination by sections, &c, of the 

 youngest herrings procurable (27 mm. long), in which the development 

 of these parts could be studied, the basal pieces appeared as paired 

 cartilaginous nodules on each side of the ventral surface of the notochord, 

 before ossification takes place generally to form the vertebral bodies, 

 and this ossification, when it does take place, forms a small bar around 

 the basal piece, without however, as we have seen, becoming completely 

 fused with it. The neural arches appear to be originally formed in 

 the same way, only that instead of forming on the anterior part only 

 of the original nodule, the remainder of which posteriorly disappears, 

 the neural ossification seems to envelop the whole nodule, which in the 

 first is smaller than the haemal basal piece. The original dorsal nodules, 

 therefore, would appear to wholly ossify as the bases of the neural arches, 

 and having, as with the haemapophyses, a bony ridge developed around 

 their bases on the vertebrae. This ridge forms the cup-shaped cavity 

 already described with which the neural arch articulates. 



The bony bars or haemapophyses developed on the basal pieces form 

 the complete haemal arches posterior to the 24th or 25th vertebra. The 

 complete arches are formed in the case of the anterior three or four, not 

 by the contiguity of the two haemapophyses directly, but by a relatively 

 strong perfectly horizontal bar (which in front of this appears on them as 

 a small sharp internal process), passing across between them slightly 

 dorsal to, i.e., within the tips of the haemapophyses, which project down- 

 wards beyond this ' bridge/ in a sharp pointed process on each side 

 (PI. XVI. fig. 6). 



The vertical parts of the haemapophysis of each side, however, gradu- 

 ally approach each other, the bridge between them becoming correspond- 

 ingly shorter and deeper. While this inclination is taking place at the 



