Page 183 - Anatomy and Physiology of Farm Animals, 8th Edition

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(A) (B)
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Figure 8-15. (A) Craniolateral view of the right stifle. a, lateral patellar ligament; b, middle patellar
ligament; c, medial patellar ligament. Red arrow indicates the direction of pull when the m. quadriceps
contracts. Through the tibial attachments of the patellar ligaments, this produces extension of the stifle.
(B) When the horse desires to “lock” the stifle in extension, the patellar is pulled proximad and turned so
that the medial patellar ligament (blue arrowheads) is looped around the medial trochlear ridge. Inset
shows a directly cranial view of this locked position.

(A) (B)

Figure 8-16. Reciprocal apparatus. Blue line, superficial digital flexor m. Red line, m. fibularis tertius.
Joint angles are denoted by the green line. Notice that when the stifle is extended (A), the origin of the
superficial digital flexor m. is pulled upward, extending the stifle by pulling on the calcaneus. The origin
of the m. fibularis tertius is rotated closer to the tibia, releasing tension on the insertion and allowing
extension of the hock. As the stifle flexes (B), tension is released on the superficial digital flexor m. but the
origin of the m. fibularis tertius is rotated further from the tibia, effectively pulling upward on the inser-
tion and thereby flexing the hock.