KNEE JOINT. 367 
out posteriorly ; where it forms three sacs, which tend to facilitate flexion 
of the joint. 
THE MovEmENTS of the elbow joint are confined to flexion and extension, 
it being a pure hinge, but these actions do not take place exactly in the 
same plane. For instance, if the knee is bent and the foot brought up to 
the elbow, the frog will not correspond with that projection, but will be 
almost entirely outside it, while the knees will also be wider apart when 
both are flexed and raised towards the bosom, than when the horse is 
standing. This arrangement is brought about by the oblique direction of 
the pulley-like articular surfaces on the humerus, ulna and radius, and 
appears to be designed to prevent the foot from hitting the opposite leg 
as it passes it in trotting. When the obliquity is insufficient, either cutting 
of the fetlocks or speedy cutting is sure to be manifested ; if too great, the 
awkward gait known as “ dishing,” is established. Extension is not nearly 
so complete as in the human subject, being limited by the greater length 
and breadth of the olecranon process, the upper part of which forms a 
prominence which fits into the corresponding fossa of the humerus, and 
thus serves as a check to the extension of the fore arm. In most men the 
upper arm and fore arm can be made to fall into one straight line, but in 
the horse there is always a considerable angle. 
THE KNEE JOINT (CARPUS, OR WRIST). 
THIS ARTICULATION is a very complicated one, and in order to under- 
stand it thoroughly, it will be necessary to examine the parts composing 
it under three divisions. Ist. The articulations between the several 
carpal bones. 2d. The Radio-carpal articulation ; and 3d. The Carpo- 
metacarpal joint, to which must be added (4) the examination of certain 
ligaments common to all three. 
THE TWO ROWS OF CARPAL BONES, which have been described in the 
dry state at page 339, are furnished with cartilage on the faces, by which 
they correspond, thus forming a series of nearly plane arthrodial surfaces, 
having synovial capsules, but embracing several of them in one. It may 
be remembered that these bones are arranged in two rows, the upper one 
consisting of the scaphoid, lunar, cuneiform and pisiform bones, while the 
lower comprehends the os magnum, the trapezoid, and the unciform bones. 
The upper row is united together by six ligaments, three anterior and 
three interosseous. The anterior ligaments consist of flattened bands of 
fibres which lie in front of the knee, and connect the four bones together, 
passing laterally from one to the other. The interosseous are strong and 
short fibres concealed between these bones, and attached to the rough 
excavations between the distinct facettes on the several bones to which 
allusion has been made at page 339, the ligament connecting the pisiform 
bone with the scaphoid being particularly well marked. 
The bones of the second row are, in a similar way, united by anterior and 
interosseous ligaments, but, instead of being three, there are only two of 
each, in correspondence with the diminished number of bones. It is 
unnecessary to describe them more minutely. 
The two rows again, between which is a partial hinge joint, are united 
by three special ligaments, in addition to those common to the whole knee 
joint, which will be presently described. ‘Two of these special ligaments 
consist of very short fibres lying behind the carpal bones, and covered by 
the great posterior ligament. The third is larger than these, and extends 
from the pisiform bone to the unciform, and to the head of the external 
