464 Prof. Reid on the Vogmarus Islandicus. 
cupied the centre of each lateral surface. The bodies of the ver- 
tebree were subcylindrical, and a transverse section of the body 
of a dorsal vertebra (fig. 3) approached an oval form, was slightly 
longer in its vertical than in its transverse diameter, and was 
considerably wider across the centre than at the upper and lower 
edges, where its processes were attached. 
The last caudal vertebra was short and terminated in, or at 
least was continuous with, a vertical plate of true cartilage, as 
proved by microscopic examination, which was thickened along 
its upper edge *. Along this thickened edge the caudal fins were 
articulated. The superior spinous processes were in general very 
slender, most of them almost thread-like, and were united 
together by a strong dense fibrous-looking membrane (fig. 3 a) 
continuous with the lamine or neural arches forming the 
spinal canal. This strong fibrous membrane was prolonged up- 
wards along the whole length of the spinous processes and also 
enveloped the lower extremities of the mterspinous or inter- 
neural spines. These interneural spines were very flexible, ap- 
peared to be of a cartilaginous texture, to the unaided eye, at 
the upper part, and of a fibrous structure at the lower part. The 
upper extremity of each became considerably expanded, chiefly 
from before backwards ; divided itself into two limbs having a 
notch between them ; and one of these limbs projected backwards, 
the other forwards, the former uniting itself to the anterior limb 
of the corresponding expansion of the interneural spine imme- 
diately behind, the latter to the posterior limb of the correspond- | 
ing expansion of the interneural spine immediately in front ; the 
whole together forming a band of true cartilage, as ascertained by 
the microscope, running along the whole length of the spine, and 
affording articular surfaces for the rays of the dorsal fin. The 
rays of the dorsal and the interspinous or interneural spines are 
articulated in this manner. On the upper surface of those parts of 
this cartilaginous band formed by the junction of the two limbs 
into which the interneural spines divide, there is a shallow arti- 
cular excavation, elongated from before backwards. Into this 
depression is fitted a cartilaginous dise secured by ligamentous 
fibres in such a manner that it is permitted to move slightly in 
all directions. The lower end of the ray of the dorsal fin bifur- 
cates, and embracing this cartilaginous disc is firmly attached to 
its lateral surfaces. The mode of articulation between the fin- 
rays and the interneural spines here described, is similar to that 
between the fin-rays and the interneural and the inferior imter- 
* This plate of cartilage ought, from its structure and relative position, 
to be regarded as formed by interneural spines. The rays of the caudal fin 
were placed close to each other at their articulation to the upper edge of 
this plate, but diverged as they proceeded outwards like the rays of a fan. 
SRLERERES DIE Hc A 
