PinkMonkey Online Study Guide-Biology
20.1 Axial Skeleton
The axial skeleton consists of the bones that form
the upright portion or axis of the body. (i.e. skull, ear
bones, hyoid bone, vertebral column, sternum and ribs).
- The Skull: The skull is formed of 28 irregularly shaped
bones (including inner ear bones). It consists of two sets
of bones cranial bones (brain case) and facial bones
(Fig. 20.2). Of the eleven paired and six single bones of the
skull, only the mandible (lower jaw bone) is movable, the
other skull bones are joined together by immovable articulations:
called sutures.
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Figure 20.2 Bones of the human skull
At birth, many cranial bones are not fused (sutured)
so that six spaces are left without any bony covering. These spaces
are called fontanels. These spaces allow change in the shape
of the child’s head in passing through the birth canal during birth,
and allow for brain growth. By the second year of development, fontanels
are completely fused.
The cranial bones (14) consist of paired
parietal, and temporal (ear ossicles)=malleus, incus, stapes) bones
and single occipital, frontal, ethmoid and sphenoid bones
The facial bones (14) consist of paired
nasal, maxillae, zygomatic, palatine, lacrimal, inferior nasal bones,
and single mandible and vomer bones.
In adult males, the skull on average is
larger, thicker and heavier, with larger air sinuses than in adult
females.
(B) Vertebral Column: (Fig. 20.3) It forms
the central axis of the body with the skull resting upon it. It
consists of 33 irregular bones called vertebrae, joined
to each other to support the trunk; it allows a good deal
of movement, provides articulation with ribs and pelvic
bones and protects the spinal cord. The vertebral column
is about 28 inches long and shows cervical, thoracic and lumbar
bends or curvatures.
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Table of Contents
20.0 -
Introduction 20.1 -
Axial Skeleton 20.2 -
Appendicular Skeleton
Chapter
21
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