47 4: Prof. Reid on the Vogmarus Islandicus. 
tion posteriorly, and in fact constitutes the chief and character- 
istic part of the tubercle. In stripping off the subjacent layer of 
the skin, some of those mimute masses constituting the chief part 
of these tubercles may adhere so firmly to it as to be torn off along 
with it. The bands forming the network are composed of fibres 
so very closely aggregated, that it is only after they have been 
mechanically separated that the fibres become distinctly visible. 
2. The lower layer of the chorion is composed of a dense areolar 
tissue assuming an aponeurotic appearance, the fibrous arrange- 
ment of which is very apparent under the microscope. These 
fibres can be readily separated from each other, and are arranged 
in two distinct layers, in each of which the fibres run parallel to 
each other, and cross those of the other layer at right angles. It is 
this aponeurotic portion of the skin which is prolonged inwards 
among the muscles to form intermuscular septa, and to assist in 
the formation of the muscular sheaths previously described. Pro- 
perly speaking this aponeurotic layer ought not to be described 
as constituting a portion of the chorion, but it is so closely united 
to it, that it requires a careful dissection to separate them. The 
difference between the. texture forming the network and the ex- 
ternal covering of the tubercles in the upper layer of the chorion, 
and the aponeurotic fibres constituting what we have just de- 
scribed as the lower layer of the chorion, is very marked when 
the polarizing prisms have been fixed in the microscope, from the 
very dissimilar colours which these two textures then exhibit. 
The skeleton did not contain any osseous texture, but was 
composed of cartilage, of fibrous tissue, and of a remarkable 
structure which was entirely new to me. ‘True cartilage was 
- found in some of the bones of the head, im the upper ends of the 
interneural spines, in the articulating discs of the dorsal fin rays, 
and in the vertical cartilaginous plate at the end of the caudal 
vertebrae. None of the vertebre contained any true cartilagmous 
tissue, except the fifty-ninth and sixtieth, in which the gelatmous- 
looking substance in the cup-shaped cavities was changed imto 
true cartilage, and which also presented the other peculiarity 
already pointed out of being considerably shorter than those im- 
mediately preceding and following them. The cartilaginous plate 
at the end of the caudal vertebra, the upper extremities of the 
interneural spines, the articulating discs of the dorsal fin rays, 
and the bones of the head previously enumerated were entirely 
composed of true cartilage, while some of the bones of the head 
were composed of true cartilage internally, and were covered ex- 
ternally by a layer of the peculiar textures about to be described. 
True cartilage, as has already been mentioned, exists in the dermo- 
skeleton, viz. in the warty-looking tubercles attached along the 
lower margin of the body of the animal. The relative amount 
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