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PinkMonkey Online Study Guide-Biology

b) Atlas vertebra (Fig. 20.6): (i) This is the first cervical vertebra and is called the ’Atlas’ because it supports the "globe" of the head. (ii) It is distinguished by an absence of body and spine and by the presence of two arches (anterior and posterior) and two lateral masses. (iii) Two lateral masses lie obliquely and connected to each other by an anterior short arch and posterior long, curved arch. (iv) The anterior arch is curved and convex with an anterior tubercle and a posterior oval or round facet for articulation with the odontoid process of the adjacent axis vertebra. (v) Transverse processes are quite long and strong, act as levers for muscles to rotate the head. (vi) foramen transversarium (for the artery) is present at the base of each transverse process.

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Figure 20.6 Atlas vertebra (Front view)

c) Axis vertebra (Figure 20.7). (i) It is the second cervical or axis vertebra distinguished by the presence of the odontoid process. (ii) The odontoid process is an approximately half-inch long, strong, tooth-like process which projects upwards. (iii) It represents the body of axis vertebra. On either side anteriorly, are small, oval facets which articulate with the facets of the atlas vertebra. (iv) The odontoid process acts as a pivot around which the atlas (with the skull) rotates. (v) Spine is large, very strong and bifid. (vi)Transverse processes are very small and do not present anterior and posterior tubercles.

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Figure 20.7 Axis vertebra (Front view)

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Table of Contents

20.0 - Introduction
20.1 - Axial Skeleton
20.2 - Appendicular Skeleton

Chapter 21


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