free booknotes online
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).

  1. 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.

Click Here To Enlarge

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.

[next page]

Table of Contents

20.0 - Introduction
20.1 - Axial Skeleton
20.2 - Appendicular Skeleton

Chapter 21


All Contents Copyright ©
All rights reserved. Further Distribution Is Strictly Prohibited.

About Us
 | Advertising | Contact Us | Privacy Policy | Home Page
This page was last updated: 10/18/2019 4:36:07 PM