350 THE HORSE. 
different structures will require a separate description ; for as the diseases 
of the joints are of great importance, a knowledge of the structure of their 
component parts must be carefully obtained ‘before SmvonLS upon the 
treatment with any hope of success. 
CARTIV.AGE. 
TRUE CARTILAGE (which is familiarly known to all when it shows the 
large white masses in a breast of veal, as dressed for the table) is a homo- 
geneous, white, semi-transparent substance, possessing a certain amount of 
elasticity, and easily cut with a knife. In the early embryo it exists as 
the sole foundation of the skeleton, bone being afterwards deposited in its 
meshes and finally substituted for it. This is called temporary cartilage. 
In after life it invests those parts of the bones which enter into the 
composition of the joints (articular cartilage, which is what we are con- 
sidering just now), and also forms the costal cartilages, the ensiform and 
cariniform cartilages, and those of the larynx, trachea, and nose. reticular 
or membraniform cartilage, differing slightly from true cartilage, is met 
with in the Eustachean tube, the external ear, and the epiglottis. 
SrructurE.—On putting a slice of true cartilage under the microscope, 
it is seen to consist of a number of minute cells disseminated through a 
vitreous substance. The cells are oval, oblong, or polyhedral in shape, 
and more or less flattened by packing. ‘The membrane forming the cell- 
wall is usually blended with the matrix, but sometimes consists of con- 
centric layers. White fibres usually inclose the mass of cells, and even 
dip sometimes into those cells more superficially placed. The cells or 
corpuscles are contained in hollow cavities, called lacune. Sometimes 
they do not entirely fill up the lacune, so that a vacant space is left. 
The corpuscles are usually dispersed in groups, varying in size and form, 
through the matrix; the groups towards the surface of the cartilage are 
generally flattened conformably with the surface. Jn articular cartilage, 
the matrix in a thin section appears dim and presents a granular aspect, 
the cells and nuclei of which are small. The parent-cells inclose two or 
three younger cells. ‘The groups they form are flattened near the surface 
and lie parallel with it. In the internal part of this cartilage the cells 
assume a linear direction, and point towards the surface. Near its 
attached surface cartilage blends with the bone, the cells and nuclei of 
which become surrounded by little granular bodies, which seem to be the 
rudimentary deposit of bone. Jn costal cartilage the cells are very large ; 
they contain two or more nuclei, which are clear and transparent, and 
some contain a few oil globules. The cells, internally situated, form 
oblong groups, disposed in lines radiating to the circumference. We 
observe a great quantity of intercellular. tissue, in the form of white 
fibrous structur e, the fibres of which are parallel and straight. 
PrriIcHoNDRIuM (epi, around, and xévépos, cartilage), is a white 
fibrous substance, which covers the external surface of all cartilages, 
except those of the joints. In this membrane the blood-vessels which 
supply the cartilage with blood, ramify. It is analogous to the periosteum 
which covers the external surface of bones. 
Nerves.—No nerves have been traced into any of the cartilages ; they 
are destitute of sensation while free from inflammation. 
BLoop-VEAsSELSs.—Cartilage is non-vascular ; it receives its nourishment 
from the bone ‘and perichondrium by imbibition. The law of endosmose 
coming into operation when the tissue is thick, as in the costal cartilages, 
