16 ON THE STRUCTURE OF TRACHYPTERUS ARCTICUS, 
The neural spines now arise further back, behind the middle of the neural plate, 
and the hemal processes originate further back still. The hemal process is now 
seen to originate from two lamellz, of which the upper gives origin to the external 
ridge, and projects beyond the general surface. 
From the ninety-second to the one-hundredth, the vertebre get smaller and 
smaller. The centra up to the ninety-fourth show two supporting ridges, and these 
go to support also the external ridges of both neural and hemal arches. These are 
reduced in the next two, and disappear in the remaining ones, and are replaced by 
irregular and slightly marked ridges. The centrum of the second last vertebra— 
the one-hundredth—is bent upwards at the middle, so that the base of one of the 
cones is inclined to that of the other. Both neural and hemal arches get gradually 
bent backwards, till the latter almost lie parallel to the axis of the vertebral column, 
each extending beyond the length of the following vertebra up to the ninety-sixth. 
Fig. 6. Tur Last Fivze VERTEBRE AND 
THE Rays OF THE CAUDAL Fin. 
r., rays of caudal fin; 7.7., rudimentary rays ; 
s., neural spine; c. 97, the centrum of the 97th 
vertebra; c. 101, the centrum of the 101st 
vertebra. (Behind and below the last vertebra 
is the cartilage which supports the caudal fin.) 
In the following vertebree it becomes shorter. In the ninety-eighth it is slightly 
expanded lengthwise; in the ninety-ninth, more so; and in the one-hundredth it 
forms a longitudinal plate beneath the latter end of the vertebra, forming at the 
same time a long tunnel beneath the vertebra. The neural spine becomes reduced 
in a similar manner, but much more so in the last two or three. In the ninety- 
third it is an inch long; in the ninety-eighth it is a short spine, one-fourth of an 
inch long; in the next two it is only represented. The neural plate has also 
undergone a slight reduction. The articular processes dwindle away, and finally 
disappear between the ninety-second and ninety-sixth vertebree. 
The last vertebra is little more than half a centrum. It consists of a cone with 
a couple of parallel ridges extending along it from base to apex in the vertical 
plane. These are evidently modified from the neural plates and the hemal 
processes. They form a groove, filled with cartilage in the recent state, which 
supports the rays of the caudal fin. 
The Interspinous Bones and Dorsal Fin Rays. 
The interspinous bones are about 173 in number, and have a similar structure 
from beginning to end, consisting of a stem, of varying length, which divides at the 
