10.29.96------start------

suspensory/stay apparatus of forelimb is today's topic

announcements: for next couple of days, ruminant and equine GI tracts 
will be out.

also, if you want to take the GIs out after hour, that's fine, just be 
sure to put them back.

note: suspensory ligaments are same in forelimb and hindlimb of the 
horse.
note: make sure you are familiar w/equine AND ruminant stuff.

note: everyone will be doing FRESH DIGITS thursday and friday.

note: in goat, be sure to look for ligaments between digits 3 and 4. 
there's a proximal ligament that ties them together.

today: hindlimb stay apparatus demo in lab.

now. stay apparatus in equine forelimb; p 295 smallwood.

center of gravity of horse behind olecranon.
center of attachment of scapula/serratus ventralis.

now, think of the foot being firmly planted on the ground. the force line 
of horse's weight passes BEHIND shoulder, THROUGH elbow, THROUGH/ANTERIOR 
to carpus, and ANTERIOR to fetlock (metacarpophalangeal joint) and 
pastern (proximal interphalangeal joint.)

so we need to prevent flexion of shoulder, and over extension of carpus, 
fetlock, and pastern.

p 241 and 239 good pics of carpus. note that the joint between the distal 
carpals and the metacarpal is flat, so doesn't bend, and there are "stop 
facets" on the proximal carpals/distal radius, which prevent 
overextension of the carpus. would have to break bone to hyperextend. 
this does occur - chip fractures of carpi. additionally, there is the 
thick palmar ligament also preventing extension.

biceps brachii goes from scapula to proximal radius, and is attached by 
the lacertus to the extensor carpi radialis. the biceps tendon is molded 
over the intertubercular groove on the proximal humerus, recall. recall 
also the intermediate tubercle within that groove. the tendon of the 
biceps is molded to fit right over that, in a unique locking mechanism. 
the biceps is also locked in position distally by the lacertus holding it 
to the extensor carpi radialis, and this tends to PREVENT flexion of the 
shoulder. see, the carpus CAN'T extend anymore for reasons already 
delineated as well as the presence of the flexor tendons on the flexor 
surface of the carpus.

what about the elbow? what's holding that up? the center of rotation of 
the elbow joint is just anterior to the collateral ligaments. the 
collateral ligaments have to be stretched to allow the flexion of the 
elbow. note also the flexors which originate on the flexor surface of the 
humerus, exerting a force on it, tending to keep the elbow in a fixed 
position. anconeus/medial head of triceps may have long-term activity 
type muscle fibers typical of postural muscle. those muscles may be used 
in stabilizing elbow, while other muscles rest.

dr orsini remarks we should cut biceps and look at fibrous band running 
through it.

understand that collateral ligament is caudal to center of rotation. to 
move the elbow you have to stretch the ligament.


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