Fig. 13.—Fifth cervical vertebra of Wolf, left side. tr., transverse process. v.a″., posterior opening of canal for the vertebral artery. pr.z. and pt.z., anterior and posterior zygapophyses. n.sp., neural spine.
Fig. 14.—First dorsal vertebra of Wolf, left side. c., centrum. r., anterior rib-facet. r″., posterior rib-facet. tr., transverse process. pr.z. pt.z., anterior and posterior zygapophyses. n.sp., neural spine.
(3) The lumbar vertebræ are almost always heavier and larger than those of the dorsal region; they carry no ribs and their neural spines and transverse processes are broad and plate-like and the latter are far larger and more prominent than those of the dorsals. As an especial degree of strength is frequently called for in the loins, together with a greater flexibility than is needed in the dorsal region, the modes of articulation between the successive vertebræ are more complex, sometimes, as in the Edentata, most elaborately so. Taking the dorso-lumbars, or trunk-vertebræ, as a single series, we may note that in a few mammals (e.g. the elephants) all the neural spines have a backward slope, but in the great majority of forms this backward inclination ceases near the hinder end of the dorsal region, where there is one vertebra with erect spine, while behind this point the spines slope forward.
Fig. 15.—Third lumbar vertebra of Wolf, front end and left side. tr., transverse process. cn., centrum. pr.z. and pt.z., anterior and posterior zygapophyses. n.sp., neural spine.
(4) The sacral vertebræ, varying from 2 to 13 in number, are fused together solidly into one piece, the combined centra forming a heavy mass and the neural canals a continuous tube, while the neural spines are united into a ridge. As a rule, only the first two vertebræ of the sacrum are in contact with the hip-bones, to support which they have developed special processes, the remainder of the mass projecting freely backward.
Fig. 16.—Sacrum of Wolf, upper side. I, II, III, first, second and third sacral vertebræ. pl., surface for attachment to hip-bone.