Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/167/
EXTREMITY. 
159 
the humerus to the scapula. The rule seems 
to be that where the pectoral extremity is chiefly 
a pillar of support, the aspect of the glenoid 
cavity is nearly vertically downwards. If free¬ 
dom and rapidity of motion be required in 
addition to strength as a member of support, 
the trunk being lighter, the scapula is oblique, 
and consequently the glenoid cavity looks 
downwards and forwards; or if the limb be 
not used to support the trunk, then the aspect 
of the glenoid cavity is no longer downwards 
but outwards, as in man. 
Structure.—The greatest part of the scapula 
is composed of very thin almost papyraceous 
compact substance ; but its processes, and the 
enlargements at its edges and angles, contain 
reticular tissue. 
Developement.—This bone is developed by 
six points of ossification; one for the body, 
and five supplementary ones, viz. one for the 
coracoid process, two for the acromion, one 
for the posterior border of the bone, and one 
for its inferior angle. The ossification of the 
body commences about the second month, and 
the spine appears in the third month as a 
growth from the posterior surface of the scapula. 
The union of the several epiphyses is not 
completed till late, and it is not until after the 
fifteenth year that the ossification is finished. 
The bones of the upper extremity, properly 
so called, are the humerus, radius, ulna, and 
bones of the hand. 
Humerus, (os brachii; Fr. l'os du bras; 
Germ, das Oberarmbein). This is the longest 
bone of the upper extremity; it is situated 
between the scapula and forearm, being, as it 
were, suspended by muscle and ligament from 
the former. 
Like all long bones, the humerus consists 
of a shaft and two extremities. The superior 
extremity is formed by a smooth and rounded 
convexity, rather less than half a sphere ; a 
slight depression in, or constriction of, the 
bone, most manifest above, marks the limit of 
this articular eminence. The eminence is 
called the head of the humerus ; the constric¬ 
tion indicates what is denominated the anato¬ 
mical neck of the bone, being that portion 
which connects the head to the shaft, and 
analogous to the more developed neck of the 
thigh-bone. The axis of the neck is but a 
continuation of that of the head, and passes in 
a direction from within outwards and down¬ 
wards, forming an obtuse angle with the axis 
of the shaft. The head of the humerus is 
entirely covered by articular cartilage, and arti¬ 
culates with the glenoid cavity of the scapula, 
to which, however, it obviously does not at all 
correspond in dimensions. 
The inferior part of the anatomical neck of 
the humerus is very slightly marked, and is 
continued in a smooth declivity slightly con¬ 
cave from above downwards, into the shaft of 
the bone. Its superior part is more distinct, 
and the depth of the groove here seems in a 
great degree owing to the prominence of two 
bony protuberances, one situated anteriorly, 
called the lesser tuberosity, and the other pos¬ 
teriorly, denominated the greater tuberosity. 
The lesser tuberosity of the humerus (tuber- 
culum minus) is somewhat conical in shape, 
and inferiorly it ends in a smooth, rounded 
bony ridge (spina tuberculi minoris), which 
extends downwards and inwards, gradually 
diminishing in prominence till it is lost in the 
shaft of the bone at the inner part of its ante¬ 
rior surface. The lesser tuberosity gives in¬ 
sertion to the tendon of the subscapularis 
muscle, and the ridge or spine last described 
forms the anterior and internal boundary of the 
bicipital groove. 
The greater tuberosity (tuberculum majus, 
externum s. posterius) forms a considerable 
prominence on the upper and outer part of 
the humerus, being the most external part in 
that situation and easily to be felt under the 
integuments. Superiorly the constriction cor¬ 
responding to the anatomical neck separates it 
from the head of the humerus ; inferiorly it is 
continued into and gradually lost in the shaft 
of the bone at its outer part. A very distinct 
and prominent ridge (spina tuberculi majoris) 
is continued from its anterior extremity down¬ 
wards and inclining very slightly inwards, 
which terminates about the middle of the an¬ 
terior surface of the bone, just internal to the 
deltoid ridge. This ridge is most prominent 
but smooth in its upper third, in its inferior 
two-thirds it is less prominent but rough; it 
forms the posterior boundary of the bicipital 
groove. On the greater tuberosity three dis¬ 
tinct surfaces are marked, to the anterior of 
which the supra-spinatus muscle is attached, 
to the middle the infra-spinatus, and to the 
posterior the teres minor. 
The bicipital groove commences above be¬ 
tween the two tuberosities, and passes down¬ 
wards and slightly inwards, bounded before 
and behind by the spines which proceed from 
those tubercles. This groove, very distinct at 
its commencement, ceases to be so a little 
above the termination of the superior third ; 
in the recent state it is lined by the tendinous 
expansion of the latissimus dorsi and teres 
major muscles, and lodges the tendon of the 
biceps muscle, whence its name. 
From the anatomical neck the bone grar 
dually tapers down and becomes more cylin¬ 
drical in its form ; this upper portion is, for the 
convenience of description, distinguished by 
the name of surgical neck of the humerus. 
The middle third of the shaft of the bone 
is prismatic in form ; the external spine 
which commences at the greater tuberosity 
is continued down, forming a prominent 
ridge all down the front of the bone to the 
termination of its flattened inferior third. The 
outer part of the middle third of the humerus 
is remarkable for the rough surface into which 
the deltoid muscle is inserted, the deltoid ridge, 
situated nearer the upper than the lower part 
of this portion, and directed downwards and 
very slightly forwards. The inner part of the 
middle third presents a smooth, flattened, and 
inclined surface, which is continued down in 
this form to within a very short distance of the 
inferior extremity of the bone. The posterior 
surface is rounded and very smooth.
        

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