OP NON-VASCULAR ANIMAL TISSUES. 
175 
circumference, and in this portion only are blood-vessels found. In some instances, 
the centre of the fibro-cartilage is entirely composed of cartilaginous corpuscles. 
The cartilaginous portion is comparatively more abundant in young than in adult 
subjects, and in the latter it diminishes as age advances. This diminution of the 
cartilaginous portion is, doubtless, to be attributed to the gradual conversion of the 
cartilaginous corpuscles into fibres. 
Of the Structure of the First Class of Fibro- Cartilages. — The Intervertebral Sub- 
stances. — I am induced to enter upon the structure of the fibro-eartilages with some 
degree of minuteness, in order to remove the vague opinions of its composition which 
have been hitherto entertained. 
I have examined the structure of fibro-cartilage in the intervertebral substance of 
the Mackerel. 
It consists for the most part of large vesicular cavities containing an aqueous hu- 
mour, in the interior of which are oil-globules and distinct nucleated corpuscles. 
The tissue in which these cavities are contained is of a fibrous character, though 
extremely lax. 
The intervertebral substance of the Cod ( Gadus Morrhua ) has a composition simi- 
lar to that of the Mackerel. 
In the intervertebral substance of the Porpoise ( Phoccena ) I observed towards its 
centre, cells of considerable size containing distinct nuclei, as well as nuclei without 
cells. Fibrous tissue in concentric circles surrounded the central soft portion. Nu- 
merous distinct cells, similar to those in the centre, were interspersed between these 
layers of fibrous tissue. The cells of the central part vary considerably in size and 
form ; some of them are double, each division presenting two central nuclei. These 
cells are round or oval ; the central nucleus which each contains, presents a distinct 
nucleolus. 
In a full-grown young Dog ( Canis Familiaris ) the intervertebral substance of the 
cervical region presents towards its centre a semifluid gelatinous mass, which is in- 
vested by a distinct capsule of fibrous substance, and from which it is easily separable. 
The gelatinous mass consists of numerous corpuscles of various sizes and in various 
stages of development. The larger ones present a granulated structure, and ap- 
pear to contain small corpuscles. The gelatinous mass also contains a small quantity 
of delicate fibrous tissue, among which the corpuscles above noticed are interspersed. 
This fibrous tissue is composed of compressed corpuscles which resemble the scales of 
the epidermis and the epithelium, each presenting a distinct nucleus, and being attached 
to its fellows by an elongated and attenuated process. Towards the circumference 
of this central gelatinous mass the fibrous tissue becomes more abundant, in the in- 
terspaces of which the corpuscles are seen. The fibres of the fibrous tissue appear to 
be formed by an elongation and growth of the corpuscles of the cartilage*. The ex- 
* Since I made this dissection the researches of M. Schwann have been published, from which he deduces the 
opinion that all tissues are developed from cells. 
