Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
notch on the internal side of the greater sigmoid 
cavity, there always occurs a mass of this sub¬ 
stance from which a production extends over 
the rough groove described above, dividing the 
sigmoid cavity transversely. 
The synovial capsule adheres closely to the 
fibrous ligaments, except where masses of adi¬ 
pose tissue are interposed, to which it is but 
loosely connected. 
Motions.—The elbow is a joint remarkable 
for possessing great solidity, which is partly 
owing to the extent of its osseous surfaces and 
the manner in which they are locked into each 
other, and partly to the strong lateral ligaments 
and the muscles which surround it. 
The motions enjoyed by the elbow-joint are 
flexion and extension. 
Flexion may vary in degree so as to be com¬ 
plete or incomplete : in complete flexion the 
fore-arm is carried forwards and inwards in an 
oblique direction across the front of the thorax, 
so as to bring the hand towards the mouth ; 
the direction of the fore-arm is determined in 
this movement by the obliquity of the trochlea 
of the humerus from behind forwards and in¬ 
wards, as described above, and influenced by 
the clavicle preventing the falling inwards of 
the shoulder ; were it not for the support of 
the clavicle, the hand in this movement, instead 
of being carried to the mouth, would be direct¬ 
ed to the shoulder of the opposite side : when 
flexion of the elbow is carried to its greatest 
extent, the coronoid process and the head of 
the radius are received into the anterior articu¬ 
lar fossæ of the humerus, displacing the adipose 
masses from these cavities, the olecranon is 
brought downwards on the trochlea so as to be 
placed below the level of the condyles of the 
humerus ; the posterior part of the synovial 
capsule, the posterior ligament, and the triceps 
and anconæus muscles are made tense, and 
applied to the adipose mass in the posterior 
articular fossa and to the posterior part of the 
trochlea : the anterior part of the capsule and 
the anterior ligament are relaxed, as are also the 
lateral ligaments. A dislocation is rendered 
impossible in this state of the articulation, 
being effectually opposed by the hold which 
the coronoid process has on the front of the 
trochlea of the humerus. 
In partial flexion or semiflexion, the several 
parts of the articulation are differently circum¬ 
stanced ; the coronoid process being carried 
down is no longer applied to the front of the 
humerus, the olecranon is on a plane with the 
condyles, and the lateral ligaments are on the 
stretch : in this state of the parts a powerful 
force applied to the olecranon from behind 
might have the effect of displacing the ulna 
forwards, were it not for the great mobility of 
the limb, owing to which a force thus applied 
is moderated or altogether expended in increa¬ 
sing the degree of flexion ; hence a dislocation 
of the ulna forwards on the humerus is an acci¬ 
dent which never happens. 
In extension, the olecranon, ascending above 
the level of the condyles, is received into the 
posterior articular fossa, displacing the adipose 
substance which previously occupied that fossa, 
the radius is brought back on the lesser head 
of the humerus, over the anterior part of which 
and of the trochlea the capsule and the anterior 
ligament are stretched ; the lateral ligaments, 
the tendon of the triceps, and the brachiæus 
anticus are also in a state of tension : the pos¬ 
terior part of the capsule and the posterior 
ligament are necessarily relaxed. It is when 
the elbow is in such a state of extension as 
here described that a dislocation of the fore-arm 
backwards usually occurs in consequence of a 
fall on the hand ; the force producing the dis¬ 
location in this case operates in the following 
way, the fore-arm serving as a fixed point, the 
humerus becomes a lever of the first order, the 
fulcrum of which is the point of the olecranon 
applied to the posterior side of its lower extre¬ 
mity, the power is represented by the weight 
of the trunk of the body applied to its superior 
extremity in front, and acting with a force pro¬ 
portioned to its remoteness from the point of 
resistance formed by the ligaments and muscles 
which are found in a state of tension in front ; 
when this force is such as to overcome the re¬ 
sistance, the ligaments in front are ruptured, 
the lower extremity of the humerus is then 
driven downwards in front of the bones of the 
fore-arm, the upper extremities of which are 
forced upwards behind the humerus, so that 
the coronoid process comes to occupy the nor¬ 
mal situation of the olecranon in the posterior 
articular fossa. 
Lateral motion. — Anatomists have been 
divided in opinion as to the possibility of any 
lateral motion being performed by the ulna on 
the humerus. Albinus, Boyer, Beclard, Cru- 
veilhier, and others, have denied the occurrence 
of it ; Monro and Bichat, however, have dis¬ 
tinctly noticed it : they consider that this mo¬ 
tion is possible only in the semifixed state of 
the elbow, when the lateral ligaments are most 
relaxed : in complete flexion, as well as in ex¬ 
tension, the tense state of these ligaments effec¬ 
tually opposes any such movement. In my 
opinion it is easy to satisfy one’s self as to the 
occurrence of this motion ; it consists of a slight 
degree of rolling of the middle prominent part 
of the greater sigmoid cavity in the fossa of the 
trochlea, produced by those fibres of the lower 
part of the triceps which extend from the con¬ 
dyle on each side to the olecranon, and by the 
action of the anconæus externally, 
(J. Hart.) 
DITION OF.—Placed in the middle of the 
long lever which the upper extremity repre¬ 
sents, the elbow-joint is of necessity exposed 
to numerous accidents, the most remarkable of 
which are fractures and luxations. These, re¬ 
duced or unreduced, produce immediate and 
remote effects, to which it is our business in 
this place to advert. Congenital malforma¬ 
tions sometimes, though very rarely, are to be 
met with affecting this articulation, and require 
some brief consideration. 
The several structures too, which enter into 
the composition of the elbow-joint, are each 
and all occasionally affected by acute and 
p 2


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