Prof. Reid on the Vogmarus Islandicus. 477 
neural spines this tube was filled up with another texture pre- 
senting an indistinct cellular appearance having some pretty 
large and distinct nucleated cells dispersed through it (fig. 7), 
approaching the cartilaginous texture, yet decidedly differing 
from it*. The walls of this tube were thinner in the superior spi- 
nous processes than in the interneural spines, and in both (figs. 7 
and 8) bands passed outwards from its circumference, which in 
the interneural spines sometimes assumed the form of the single 
chain, similar to what has been represented in fig. 4. Quadri- 
lateral and hexagonal hyaline tubes, combined with a greater or 
less proportion of the fibrous and nucleated tissue which fills up 
the intervals between the rays in the body of the vertebree, enter 
into the formation of many of the bones of the head, while por- 
tions of some of them, as the nasal processes of the intermax- 
illaries, and portions of the body of the sphenoid, and the ante- 
rior sphenoid, and some parts of the superior maxillary, are en- 
tirely composed of these tubes closely aggregated together. Se- 
veral bones which consist internally of true cartilage, as those 
composing the posterior, lateral and superior walls of the cranium, 
the hyoid and inferior maxilla, are covered externally by a layer 
of these tubes intermixed with the fibrous and nucleated tissue. 
In the bones of the cranium this covering is confined to the ex- 
ternal surface. The branches of the superior maxilla which go 
to join the inferior maxilla are not covered by skin, but by a dense 
firm layer made up of these tubes. This tubular structure also 
abounds in the branchial arches, ithe scapular arch, in the 
opercular bones, and in the branchiostegous rays, all of which 
structures are destitute of true cartilaginous and osseous tissues. 
EXPLANATION OF PLATE XVI. 
Fig. 1. Part of the digestive tube slit open. The commencement of the 
large intestine has been detached and separated from the posterior 
end of the stomach: a, pyloric portion of stomach ; 6, cul de sac 
of stomach; ¢c¢, second portion of small intestine; d, ceca sur- 
rounding duodenum or first portion of the small] intestine ; /, duo- 
denum ; g, lower portion of cesophagus ; h, valve at the termina- 
tion of the small in the large intestine ; m, commencement of large 
intestine; 0, spleen. 
Fig. 2. Fibres, greatly magnified, from the external surface of the skin, upon 
which its silvery lustre depends. 
Fig. 3. Transverse section of an abdominal vertebra. 
figs. 4,5 and 6. Representations greatly magnified of a peculiar hyaline 
tissue entering largely into the formation of the skeleton. 
Fig. 7. meant structure seen in a transverse section of the interspinous 
ones. 
Fig. 8. Peculiar structure seen in a transverse section of the spinous pro- 
cesses of the vertebree. 
_ * The smaller tubesformed by this dense hyaline substance, such as those 
in the bodies of the vertebrae, in some instances, if not in all, contain more 
or less of a soft substance without any distinct structure in which some gra- 
nules are imbedded. 
