THE NORTHERN RIBBON-FISH. 15 
The fifth to the fortieth have all a structure which answers to the typical 
description given above. The neural spine is very slender, being only 0013 to ‘0015 
inch in. thickness. Near the arch it is a flattened band of this thickness. The 
spines gradually increase in length. This increase may be seen in Fig. 10, Pl. II. 
At first they are curved backwards, but become gradually straighter and more erect 
as we pass back. The centra likewise show the gradual increase in length already 
referred to. The hemal processes have the typical structure, the external ridge 
and anterior expansion, and are seen to increase in length up to the eighteenth, and 
then decrease in the succeeding two or three to a size which remains pretty constant 
in the group we are considering (PI. II., Fig. 10). The first hzemal process (in the 
fourth vertebra) is directed downwards and obliquely backwards; the succeeding 
ones are reflected more and more downwards. 
In the forty-first vertebra the hemal process is found to be directed much 
more backwards, and at the same time greatly lengthened, and the extremities 
approximated. The latter meet and fuse in the forty-fourth and the following ones, 
that is to say, behind the ureter. The inner edges meet and are produced together 
into a heemal spine, in which the individuality of the two transverse processes remains 
distinct for some way. The hzemal arches are directed gradually more and more 
backwards. 
The svxty-fifth vertebra lies over the end of the body cavity. The centrum is 
now half-an-inch long. The neural spine reaches its maximum in this region, being 
about three and a-half inches long, and so does the heemal spine, which is two inches . 
long. The centrum presents fewer strengthening lamellae. The spines are com- 
paratively strong—nearly one-twentieth of an inch in diameter. The neural plate is 
long, corresponding to the increase of length of the centrum. It has remained of a 
nearly constant height throughout. 
Between the sixty-fifth and ninety-second vertebre we find the increase in 
length of the centra gradually culminating at the same time that they become 
reduced vertically. At first four radiating lamelle are found between the neural 
and heemal processes, but these become reduced to three in the first few vertebrze 
of this group, and this number remains fairly constant till about the eightieth, 
when only two are found. Moreover, the double fossa enclosed by the heemal arch gets 
replaced by one in about the first six of this group—the median ridge having dis- 
appeared. The neural and hemal spines gradually decrease in size, and towards the 
end of the group become inclined more and more backwards ; both remain of a pretty 
uniform thickness throughout. The neural plate also becomes reduced in height 
gradually. 
The articular processes in the sixty-fifth are perfectly normal, but as we trace 
the series backwards we find that the anterior is gradually rounded off, while the 
posterior zygapophysis remains prominent, but in the last four or so of the group the 
latter also become reduced. ; 
