In the Megatheriidae as in the sloths the neural spines are all directed backwards, and in the lumbar region additional articulating surfaces occur, better developed than are those in Bradypus.
In the ant-eaters (Myrmecophagidae) there are seventeen or eighteen thoraco-lumbar vertebrae, all of which except two or three bear ribs. The posterior thoracic and anterior lumbar vertebrae articulate in a very complex fashion, second, third, and fourth pairs of zygapophyses being progressively developed in addition to the ordinary ones, as the vertebrae are followed back.
In the Armadillos the lumbar vertebrae have long metapophyses which project upwards and forwards and help to support the carapace. In Glyptodon almost all the thoraco-lumbar vertebrae are completely ankylosed together.
In the Manidae there are no additional zygapophyses but the normal ones of the lumbar and posterior thoracic regions are very much developed, the postzygapophyses being semi-cylindrical and fitting into the deep prezygapophyses of the succeeding vertebra.
In the Sirenia the number of lumbar vertebrae is very small; in the dugong there are nineteen thoracic and four lumbar, and in the manatee seventeen thoracic and two lumbar.
In the Cetacea the number of thoracic vertebrae varies from nine in Hyperoödon to fifteen or sixteen in Balaenoptera, and the number of lumbar vertebrae from three in Inia to twenty-four or more in Delphinus. The lumbar vertebrae are often very loosely articulated together and the zygapophyses sometimes as in the Dolphins are placed high up on the neural spines. The centra are large, short in the anterior region but becoming longer behind. The epiphyses are prominent, and so are the neural spines and to a less extent the metapophyses. The transverse processes are well developed, anteriorly they arise high up on the neural arch, but when the vertebral column is followed back they come gradually to be placed lower down, till in the lumbar region they project from the middle of the centra. This can be well traced in the Porpoise (Phocaena). In the Physeteridae the transverse processes of the anterior thoracic vertebrae are similar to those of most Cetacea, but when followed back, instead of shifting their position on the vertebrae, they gradually disappear, and other processes gradually arise from the point where the capitulum of the rib articulates.
Ungulata. In the Ungulata vera the thoraco-lumbar vertebrae are slightly opisthocoelous. The anterior thoracic vertebrae commonly have exceedingly high backwardly-projecting neural spines (fig. 89, 1); but those of the lumbar and posterior thoracic vertebrae often point somewhat forwards so that the spines all converge somewhat to a point called the centre of motion (cp. fig. 101). In the Artiodactyla there are always nineteen thoraco-lumbar vertebrae, and in the Perissodactyla twenty-three.
Procavia sometimes has thirty thoraco-lumbar vertebrae, a greater number than occurs in any other terrestrial mammal; twenty-two of these are thoracic and eight lumbar. In Phenacodus the convergence of the neural spines to a centre of motion is well seen.
Fig. 89. First and second thoracic vertebrae of an Ox