The _Atlas_ is a bony ring composed of two arches, an anterior and a posterior, separated in the recent state by a transverse ligament. Its body is detached and appears as a tooth-like projection upward from the body of the Axis, the odontoid process, which articulates with the anterior arch of the Atlas and around which the Atlas rotates, a ring around a pivot. The Atlas supports the head upon its lateral masses, two wedge shaped bodies between the anterior and posterior arches, thinner internally than externally. It has no spinous process but merely a tubercle where the laminae join, so that it can be palpated only from the sides upon the tips of its long transverses. The first Cervical, or suboccipital, nerves emerge by a groove above the pedicles instead of through a foramen. The _Axis_, or second Cervical, is distinguished by its large, strong spinous process, which is bifid at its tip, by its superior articular processes which rest upon body, pedicles, and transverses, and by its odontoid process, upreared from the body. The _Seventh Cervical_, or Vertebral Prominens, usually has a large spinous process, presents no foramina in its transverse processes, or only one, the left, and shows no facets on body or transverse for the rib articulation, as do the Dorsals. The _Sacrum_ is the largest vertebra; is curved with its convexity backward; is commonly made up of five fused segments; has only rudimentary spinous and transverse processes except the first; and shows sixteen openings, eight anterior and eight posterior, or four on either side of the median line in front and the same number and arrangement behind. These openings permit the exit of the anterior and posterior primary divisions of the sacral nerves separately. The _Coccyx_, usually composed of four fused segments, is a triangular bone which articulates with the Sacrum above and is free at its distal extremity. Its portion of the neural canal is open posteriorly and contains merely the thread-like termination of the cord membranes. It is frequently ankylosed to the Sacrum, sometimes in an abnormal position so as to impinge the single pair of coccygeal nerves. The different regions of the spine show decided differences in structure, though all resemble each other. The Cervicals are smallest, the Dorsals next in size, and the Lumbars largest and strongest of the movable vertebrae. The Dorsals have facets and demi-facets for the articulation of the twelve pairs of ribs with their bodies and intervertebral substance, as well as oval facets upon the anterior aspect of their transverses for articulation with the tubercles of the ribs.