Shoulder Clavicle (1)
Carpal bones (8)
Metacarpal bones (5)
Fig. 1,1: Parts and 32 bones of the upper limb
EVOTUTION OF UPPER TIMBS
The forelimbs have evolved from the pectoral fins of
fishes. In tetrapods (terrestrial vertebrates), all the four
limbs are used for supporting body weight, and for
locomotion. In arboreal (tree-dwelling) human ances-
tors, the forelimbs havebeen set free from their weight-
bearing function. The forelimbs, thus 'emancipated',
acquired a wide range of mobility and were used for
prehension or grasping, feeling, picking, holding,
sorting, breaking, fighting, etc. These functions became
possible only after necessary structural modifications
such as the following, were done:
a. Appearance of joints permitting rotatory movements
of the forearrns (described as supination and
pronation), as a result of which food could be picked
up and taken to the mouth.
b. Addition of the clavicle, which has evolved with the
function of prehension.
c. Rotation of the thumb through 90 degrees, so that it
can be opposed to other digits for grasping.
d. Appropriate changes for free mobility of the fingers
The primitive pentadactyl limb of amphibians,
terminating in five digits, has persisted through
Fig.1.2: Scheme of skeleton of upper limb showing lines of
evolution and is seen in man. Ih some other species,
however, the limbs are altogether lost, as in snakes;
while in others the digits are reduced in number as in
ungulates. The habit of brachiation, i.e. suspending the
body by the arms, in anthropoid apes resulted in
disproportionate lengthening of the forearms, and also
in elongation of the palm and fingers.
Study of Anotomy
In studying the anatomy of any region by dissection, it
is usual to begin by studying features of the skin, the
superficial fascia and its contents, and the deep fascia.
This is followed by the study of the muscles of the
region, and finally, the blood vessels and nerves. These
descriptions should be read only after the part has been
dissected with the help of the steps of dissection
provided in the book.
Before undertaking the study of any part of the body,
it is essential for the students to acquire some
knowledge of the bones of the region. It is for this reason
that a chapter on bones (osteology) is given at the
beginning of each section. While reading the chapter,
the students should palpate the various parts of bones
on themselves. The next chapter must be studied with
the help of loose human bones.