Williams, Fisher, and Udall: The Spavin Group. 23 
in defective elasticity unless specially posed, while in the horse 
the long axis of the limb describes great alternating angles, the 
scapulo-humeral opening backwards, the humero-radial forwards, 
and the phalanges extending obliquely downwards and forwards 
from the metacarpus. When a horse places its weight upon the 
end of the last phalanx, the smallest base of support seen in any 
mammal, the very narrowness of that support, combined with the 
angles in the limb and especially the obliquity of the pastern, 
serves to almost entirely prohibit lateral impact, and any violence 
- tends rather to decrease the angles and shorten the limb. As 
a result dislocation and strain are well-nigh unknown, and the 
lateral articular ligaments in the horse are comparatively small 
except in the scapulo-humeral articulation, where passive liga- 
ments are replaced by powerful muscles which permit of a con- 
siderable normal displacement of the articulation without injury. 
It thus occurs that lateral or median luxation in its ordinary 
meaning almost never takes place anywhere in the anterior limb 
of the horse whereas it is comparatively frequent in the arm of 
man, not an articulation escaping. 
The mechanism to prevent antero-posterior luxation in the 
horse is highly developed, the powerful biceps assumes the role 
of a great musculo-tendinous band to retain the scapulo-humeral 
articulation in front while the anconean group of muscles pre- 
vents the sufficient opening of the angle behind to admit of 
posterior luxation and at the same time the two muscles guard, 
in a reverse manner, the humero-radical articulation. Beyond 
these, the great flexor muscles and their powerful tendons serve 
as elastic supports upon which the articulations rest securely 
behind with little need for posterior ligaments and with the 
weight ever inclining backwards upon these tendons to such a 
degree that almost no provision is required against anterior dis- 
placement, or anterior strain. , 
In man, on the other hand, the great freedom of movement 
in every direction, including rotation, submits each and every 
joint to overtension of its ligaments. They may become strained 
or may rupture and luxation follow, or the ligaments may prove 
too resistant and the bones become fractured. Anatomically 
strains and luxauons and fractures resulting therefrom should 
be common in man and very rare in the horse. Clinically we 
observe these quite commonly in the thoracic limb of man and 
abundant strains which do not end in luxation or fracture, but are 
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