Fig I. ATLAS (supero posterior surface).

Fig I. ATLAS (supero-posterior surface).

1. Wing.

2. Supero-anterior foramen.

3. Postero-inferior foramen.

4. Surface for articulation with axis.

5 Inferior tubercle or inferior spinous surface. 6. Spinal canal.

Fig. 2. ATLAS (antero  inferior surface).

Fig. 2. ATLAS (antero- inferior surface).

1. Wing. 2. Postero-inferior foramen.

3. Facet for articulation with condyles of occiput.

4. Inferior tubercle or inferior spinous process.

5. Spinal canal.

Fig. 3. AXIS (side view).

Fig. 3. AXIS (side view).

1. Superior spinous process. 2. Intervertebral foramen. 3. Transverse process.

4. Odontoid process.

5. Inferior spinous process.

6. Posterior articular face of body.

7 Oblique process.

Fig. 4. DORSAL VERTEBRA (front view).

Fig. 4. DORSAL VERTEBRA (front view).

1. Superior spinous process. 2. Transverse process. 3. Articulation for tubercle of rib. 4. Articulation for bead of rib. 5. Anterior articular face of body. 6. Spinal canal.

Fig. 5. DORSAL VERTEBRA,side view.

Fig. 5. DORSAL VERTEBRA,side view.

1. Superior spinous process. 2. Facet for articulation of tubercle of rib. 3. Posterior articular process, 4. Facet for articulation of head of rib. 5. Intervertebral notch 6. Body. 7. Posterior articular surface of body. 8. Anterior articular surface of body.

Behind is a large single articular surface with which it is united to the second bone or axis. The spinal opening in this bone is of considerable size, in order to permit the extensive and varied movements of the head upon the neck without injury to the spinal cord.

The Axis (fig. 3, Plate XXXVIII) or second bone of the neck is so called because it serves as a pivot on which the head is moved from side to side. The pivot is provided by a process of bone (odontoid process) which proceeds from the anterior extremity of the body and passes into the ring of the atlas which is in front of it. This bone differs from the other cervical vertebras, in the large size and strength of its superior spinous process, the small size of the transverse processes, and the presence of only two oblique processes, which are behind.

The remaining five cervical vertebras are (dis-tinguished numerically as the 3rd, 4th, 5th. 6th, and 7th (fig. 283), and although each possesses some minor distinctive feature, it is not necessary to dwell upon them here.

The Dorsal Vertebrae (fig. 284) present a good deal in common. Some of them, however, are readily distinguishable from the others by the length of the superior spinous processes. This is especially the case with regard to the first eight bones. Of these the length in-creases to the fifth, and then gradually diminishes backward.

The Lumbar Vertebrae (fig. 285) are distinguished from those above described in the much greater length and width of their transverse processes, which are directed horizontally outwards. The last two are much thicker and somewhat shorter than the rest, and are united to each other by the borders of their transverse processes, and to the transverse process of the sacrum by synovial articulations.

Cervical Vertebra.

Fig. 283. - Cervical Vertebra.

1 Articular Head. - Vertebral Foramen. 3 Transverse Process. 4 Spinal Canal. 5 Anterior Articular Process. 6 Inferior Spinous Process.

Dorsal Vertebra (Front View).

Fig. 284. - Dorsal Vertebra (Front View).

1 Superior Spinous Process. 2 Transverse Process. 3 Articulation for Tubercle of Rib. 4 Articulation for Head of Rib. 5 Anterior Articular Face of Body. 6 Spinal Canal.

Lumbar Vertebra.

Fig. 285. - Lumbar Vertebra.

1 Superior Spinous Process. 2 Anterior Oblique Process. 3 Transverse Process. 4 Anterior Articular Face of Body. 5 Spinal Canal.

The Sacrum (fig. 286) or rump bone, as we have already pointed out, is a large single triangular bone in the adult, resulting from the welding together of five vertebrae, which are separate in the foetus. It forms that part of the body termed the croup, and is fixed like a wedge between the dorsal spines of the ossa innominata or hip bones.

Sacrum (Side View).

Fig. 286. - Sacrum (Side View).

11 Superior Spinous Processes. - Transverse Process. 3 Articulation for Last Lumbar Vertebra. 4 5 6 7 Superior Sacral Foramina for the passage of the Superior Sacral Nerves.

The Coccygeal Vertebrae, or tail-bones, are from fourteen to eighteen in number. The first three or four partake very much of the character of true vertebrae, being wanting only in the oblique processes. In the remainder of the tail-bones the proper vertebral characters gradually become more and more obscure until they altogether disappear.

Most of the bones of the spine present some peculiarity of form by which they may be distinguished one from another; but enough has been said to give the reader a general idea of their characters.