Download DRAWING AND DESCRIPTION OF GIRDLE BONES – PART 2

DRAWING AND DESCRIPTION
OF GIRDLE BONES – PART 2
(PELVIC GIRDLE)
The basic requirements for drawing a bone include a ruler, a well sharpened pencil, a
rubber (eraser) and a drawing sheet of appropriate size corresponding to the size of the note
book. Before we directly start drawing the bone, first of all draw the bordering line on the
paper where the drawing is to be made. Then, after drawing the borderline, just on the right
hand top corner below the borderline you should keep a space for writing the date on which the
diagram is drawn. Along with it in the middle portion just below the borderline you have to
write the name of the bone. After that you make a virtual division of the drawing sheet, so that
the required views of the bones can be drawn proportionately in each division. As for example
if you want to represent the anterior, posterior, medial and lateral views of the bone then divide
the drawing sheet into four virtual divisions wherein you can draw one view each. Thereafter,
you can start drawing in a systematic way.
The drawing should be purely free hand drawing. However, it should be proportionate to
the original bone. That means it should neither be very large nor very lengthy. You can use
slight shading of various parts of the bone like condyles, facets, tuberosities, tubercles, fossa,
foramen, ridges, crests etc. so that the same is very clearly and distinctly visible. After
drawing, the next step is to label the various parts of the bone. You should as far as possible
use dotted lines in labelling the various parts because solid lines may often be confused as a
part of the bone. Then after labelling various parts of the bone you also have to labelled the
various views you have drawn such as anterior view, posterior view, profile view, inferior view
etc. And after labelling provide a space for the teacher’s remark and signature at the bottom
right or left hand corner just above the border line.
For a systematic description of the bone, first of all, you should carefully observe the bone, and
identify the type of skeleton, part of skeleton, type of bone by stating reasons, and also
anatomical position and location in the skeleton. Then you can start elaborate systematic
description of various parts of the bone.
Systematic description of hip bone
Type of skeleton :
Endoskeleton as it is found underneath the tissue
Part of skeleton :
Appendicular part as it is the bone of lower extremity
Type of bone :
An irregular bone, because it has an irregular shape
Location :
Located at the hip region of human body
Name of bone :
Human hip bone (innominate bone)
General Description
The hip bone is a large, flattened, irregularly shaped bone, constricted in the centre and
expanded above and below. It meets its fellow on the opposite side in the middle line in front,
and together they form the sides and anterior wall of the pelvic cavity. It consists of three parts,
ilium, ischium, and pubis, which are distinct from each other in the young subject, but are
fused in the adult. The union of the three parts takes place in an around a large cup-shaped
articular cavity, the acetabulum, which is situated near the middle of the outer surface of the
bone. The ilium is the superior broad and expanded portion which extends upward from the
acetabulum. The ischium is the antero-posterior and strongest portion of the bone which
proceeds downward from the acetabulum and expands into a large tuberosity, and then curving
forward to meet with the pubis. Pubis is the anterior-inferior part of hip bone. Two hip bones
articulate with each other anteriorly at pubic symphysis. Anterolaterally it articulates with
femur, and posteriorly with sacrum.
Anatomical Description of various parts
Hip bone is a bone lying inside the body covered by muscles. Therefore, it is an endoskeleton. It is included in appendicular skeleton because it is the part of lower limb. Being
irregular in shape, it is an irregular bone. Hip bone also called innominate bone is formed by
fusion of ilium, ischium and pubis.
Ilium forms the upper expanded fan like shaped body and 2/5 of the bony structure which
form a part of the acetabulum. It has therefore two-ends. One is an iliac-crest and the other end
formed by 2/5 of the acetabulum. Ilium has three surfaces -anterior surface, which faces
towards the front, the other surface is the gluteal surface (facing back) and the third surface is
sacro pelvic surface. This surface is covered by sacrum, so, known as call sacro-pelvic surface.
The Ischium forms the lower and back part of the hip bone. It is divisible into three portions—
a body and two rami. The body enters into and constitutes a little more than two-fifths of the
acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a
portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it
gives origin to some fibres of the obturator internus. Its anterior border projects as the
posterior obturator tubercle. From its posterior border there extends backward a thin and
pointed triangular eminence, the ischial spine, more or less elongated in different subjects.
Above the spine is a large notch, the greater sciatic notch. Below the spine is a smaller notch,
the lesser sciatic notch.
The pubis- the anterior part of the hip bone, is divisible into a body, a superior and an inferior
ramus. The body forms one-fifth of the acetabulum, contributing by its external surface both to
the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the
wall of the lesser pelvis and gives origin to a portion of the obturator internus. The superior
ramus (ascending ramus) extends from the body to the median plane where it articulates with
its fellow of the opposite side. It is conveniently described in two portions, viz., a medial
flattened part and a narrow lateral prismoid portion. The inferior ramus (descending ramus) is
thin and flattened. It passes lateralward and downward from the medial end of the superior
ramus. It becomes narrower as it descends and joins with the inferior ramus of the ischium below
the obturator foramen.
The cup shaped deep hemispherical cavity formed at the junction of fusion of ilium, ischium and
pubis is called acetabulum. The area cover by these three bones at acetabulum is 2/5, 2/5 and
1/3 respectively. In other words 2/5 parts of ilium, 2/5 parts of ischium and 1/5 parts of pubis
forms the acetabulum. It is through which, head of femur articulates. However, the whole of this
acetabulum is not articulatory. When we observed carefully there is a horse-shoe shaped
structure inside the acetabulum. This surface is the articulatory surface. So it has an articulatory
and non-articulatory surface. In human male adult, this acetabulum is having an area of about
22.5 sq.cm. and for female it is less than 22.5 sq.cm.
Side identification
To identify the side of the bone the following characteristics should be kept in mind. The ilium
bone should be antero-medial in position. It should face anteriorly forward and at the same time
medially. So it should be antero- medial. The pubis should be anterior and should not face
backward. Hollow cavity of obturator foramen should lies in inferior position. Keeping it in this
position and at the same time the acetabulum lying on the lateral side, we can very easily identify
the side of the bone.
Conclusion
Why are we drawing and describing human bones? 1. To identify the bones, 2 To know its
anatomical description, its location, and how it articulates along with other bones. 3. By knowing
the procedure of drawing and description of human bones, we can go for comparative anatomy,
comparison of bones, structure of various parts of bones of human beings as compared to other
animals, mammalian animals and mammalian primates. So as a student of anthropology it is a
must for all to know how to draw and describe the bones.