RUPTURE OF THE FLEXOR TENDONS AND SUSPENSORY LIGAMENT. 567 
generally caused by jumping obstacles. Sometimes the flexor pedis 
perforans is affected, though the suspensory ligament may also be 
ruptured. Fig. 210 is drawn from a case of rupture of the suspensory 
ligament in a race-horse which fell lame on the race-course and had been 
unsuccessfully treated for a long time. 
A careful inspection of instantaneous photographs of moving horses 
(like those of Marey or Muybridge) shows that in galloping and in 
landing from a jump the animal’s whole weight rests for an appreciable 
time on one of the fore limbs. At this moment the fetlock is supported 
by the contraction of the flexor pedis perforans and perforatus muscles, 
which are elastic, and by the passive resistance of the suspensory 
ligament, which is comparatively inelastic. Should, then, the strain 
thrown on the limb exceed the elastic resistance of the muscles, either 
they or their tendons must necessarily yield. One of two results may 
follow. If the muscles yield, the excess strain falls on the comparatively 
inelastic suspensory ligament, which maybe partially or wholly ruptured. 
If the tendons yield, a similar result may follow, the flexor tendons and 
the suspensory ligament then suffering together. A single very violent 
shock is therefore more likely to affect both the tendons and ligament 
(because the muscles being untired do not yield), while long-continued 
exertion is favourable to strain of the suspensory ligament alone, on 
account of the muscles relaxing and the pull on the tendons never 
becoming sufficient to overcome their tensile strength. In the latter 
case the excess strain necessarily falls entirely on the suspensory 
ligament. The fact that strain of the suspensory ligament is practically 
confined to the front legs in all riding horses is explained by the fact 
that an unduly large proportion of the rider’s weight falls on the fore 
limbs, and that this proportion tends to increase with increase in speed. 
Rupture of the flexor tendons often coincides with disease of their 
surface at the point where they respectively pass over the sesamoids or 
navicular bone, a change which commonly accompanies chronic navicular 
disease and suppuration in the fibro-fatty frog, terminating in necrosis 
of the flexor pedis perforans. Rupture of the flexor perforans and 
perforatus often follows purulent inflammation of their tendon sheaths 
and of the gliding surface of the sesamoid bones. In such cases rupture 
is due to inflammation in the sheaths of the tendons; it is favoured by 
neurectomy. Fig. 209 shows an almost complete rupture of the flexor 
pedis perforans behind the fetlock, consequent on purulent disease of its 
sheath. During navicular disease the gliding surface of the navicular 
bone becomes rough and produces erosion of the perforans tendon; the 
peculiar cases following neurectomy result from violent over-extension of 
the tendon. 
Moller describes cases where the perforans and perforatus tendons in 
