The Perissodactyla have remarkably opisthocoelous cervical vertebrae. Those of Macrauchenia have the posterior half of the vertebrarterial canal confluent with the neural canal as in Tylopoda. In the Proboscidea they are short flattened discs slightly opisthocoelous; the axis and seventh vertebra and to a less extent the sixth have high neural spines.
In the Rodentia the atlas generally has broad wing-like transverse processes, and the axis a large and long neural spine, while the odontoid process is much developed. In the Jerboas (Dipus) all the cervical vertebrae except the atlas are fused together, a condition recalling that in armadillos.
In the Carnivora the wings of the atlas are well developed (fig. 69, A, 1), and it is deeply cupped for articulation with the condyles of the skull. The axis has a long odontoid process and a high compressed neural spine (fig. 69, B, 4). The third to sixth cervical vertebrae have large transverse processes with prominent perforated inferior lamellae, whose ventral margins in the third and fourth vertebrae diverge as they pass backwards, while in the fifth they are parallel and in the sixth convergent. The transverse processes of the seventh vertebra have no inferior lamellae and are not perforated. Metapophyses are often developed.
In the Insectivora the cervical vertebrae vary considerably. The neural spines except in the case of the axis are generally very small and in the Shrews and Moles the neural arches are exceedingly slender.
In the Chiroptera all the cervical vertebrae are broad and short with slender neural arches.
Primates. In Man the cervical vertebrae have short blunt transverse processes and small often bifid neural spines. The neural and vertebrarterial canals are large. The atlas forms a ring surrounding a large cavity, and has a very slender inferior arch and small transverse processes. Traces of a pro-atlas have been described in Macacus and Cynocephalus. The axis has a prominent spine and odontoid process and short transverse processes. In most Primates the cervical vertebrae are very similar to those of man, but the inferior lamellae of the transverse processes are better developed. In the Anthropoid Apes the neural spines are as a rule much elongated.
Thoraco-lumbar, or Trunk vertebrae.
In the Monotremata there are nineteen thoraco-lumbar vertebrae, sixteen (Echidna) or seventeen (Ornithorhynchus) of which bear ribs. The transverse processes are very short and do not articulate with the ribs, which are united to the centra only.
In the Marsupialia there are always nineteen thoraco-lumbar vertebrae, thirteen of which generally bear ribs. The lumbar vertebrae frequently have large metapophyses and anapophyses, these being specially well seen in the Kangaroos and Koala (Phascolarctus).
The Edentata are very variable as regards their trunk vertebrae. The two genera of Sloths differ much as regards the number, for while Bradypus has only nineteen, fifteen or sixteen of which bear ribs, Choloepus has twenty-seven, twenty-four of which are thoracic, and bear ribs. In Bradypus a small outgrowth from the transverse process articulates with the neural arch of the succeeding vertebra. In both genera the neural spines are all directed backwards.