CONTRIBUTIONS TO ZOOLOGICAL PATHOLOGY. 207 
and point towards the surface. This arrangement is probably 
connected with a corresponding peculiarity of texture of the inter- 
cellular substance; and hence is caused the vertical appearance 
presented by the laminae generally*. 
The synovial membrane is extremely thin, and invests the 
whole of the interior of the articular surface. Like the generality 
of serous membranes, it forms a complete shut sac — one surface of 
which is rough and attached to the parietes of the joint, and the 
other, being smooth and free, secretes the viscid, stringy matter — 
the sjmovia, or joint-oil. In its intimate structure, it is formed of 
dense compacted fibres of cellular substance, having its inner or 
free surface covered with a pavement of tesselated epithelial cells. 
These epithelial cells, or plates, are easily seen on that part of the 
membrane which is attached to the ligament; and, a few years ago, 
Henlet also shewed their existence upon the entire cartilaginous 
surface, thereby proving, beyond a doubt, that this membrane is 
continued over the entire surface of the articular cartilage, a cir- 
cumstance which has been for a long time questioned. Their 
existence in this situation is best demonstrated in the earlier 
periods of life; for, as age increases, they become removed or 
rubbed off from the basement synovial membrane by the in- 
creased activity which then takes place in the functions of the 
joint. 
In regard to the sulci, or the deficiency in the development of 
the cartilaginous lamellae, they are always found at opposing 
points, and in both bones, along the centre of the articulation. In 
the hock-joint they are superior to the central axis of revolution of 
the joint. When either of their surfaces, in the very recent 
state, are examined by a simple magnifying glass, the margins of 
the depressions, instead of presenting the compact, smooth, clear, 
and glistening appearance of the general surface of the cartilage, 
will, on the contrary, be found to have a dull and rather grooved 
or porous aspect, as if the cartilaginous lamellae had been disjoined 
from each other. This porous and pulpy appearance is greatest 
at the very margin of the sulcus ; for, externally, it becomes 
gradually lost in the surrounding cartilage. From the pointed 1 
extremities of the sulcus, especially in that of the astragalus, an 
irregular winding groove, formed by an opening out of the lamellae, 
will be found to extend along the centre of the articular groove to 
the upper and lower part of the articulation. 
In the depression itself, there is a distinct and variable deficiency 
in the depth of the vertical lamellae ; the surface is irregular, rough, 
* Vide, also, Tod and Bowman’s Physiological Anatomy, part i, p. 90. 
f Henle, in Muller’s Archives fur Anatomie, page 116. 1838, 
