On either side of the spinous processes is a =vertebral groove= which contains the deep muscles of the spine. The floor of the groove is formed by the laminæ and articular processes. It is wide in the neck and narrows progressively in the back. Viewed from the side, the column presents a series of curves. When the head and neck are in the ordinary neutral position, the anterior part of the cervical spine forms a gentle curve, concave ventrally. The posterior cervical and first thoracic vertebræ form a more pronounced curve in the opposite direction. At the junction of the cervical and thoracic regions there is a marked change of direction, forming a ventral projection or angle. At the second thoracic vertebra a gentle curve, concave ventrally, begins. This is continued to the lumbo-sacral junction, where there is a change of direction, and hence a promontory. The sacrum has a variable, but never very pronounced, ventral concave curvature, which is continued in a much accentuated form in the coccygeal region. It may be remarked that a line through the summits of the spines does not correspond to these curves formed by the bodies. The =vertebral canal=, of course, corresponds in curvature to the bodies. Its =caliber= varies greatly at different points. The greatest diameter (ca. 5 cm.) is in the atlas, where it contains the dens of the axis in addition to the spinal cord, and provision must be made for extensive movement. It is very much smaller in the axis (ca. 2.5 cm. wide, 3 cm. high). It widens considerably at the junction of the cervical and thoracic regions to accommodate the cervical enlargement of the spinal cord. Beyond this it diminishes, and is smaller in the middle of the back than at any preceding point; this is correlated with the small size of the spinal cord and the very limited movement of the spine. At the middle of the lumbar region it again widens considerably to contain the lumbar enlargement of the spinal cord. The caliber diminishes very rapidly from the second sacral segment backward, and the canal ceases to be complete at the fourth coccygeal vertebra. The =articular processes= are very large and wide apart in the neck, greatly reduced and much closer together in the back, larger and interlocking in the lumbar region.