it environs the cerebrum, from which these nerves originate. The nasal vertebra contains the olfactory nerves. 2113. Each cranial sense has thus only one vertebra, and the skull will consequently be formed of four vertebræ, whereof three appertain to the cranium, one unto the face. (See Oken's Ueber die Bedeutung der Schädelknochen, 1807.--Isis, 1817, S. 1204.) 2114. Several vertebræ are, however, found for the sense of feeling or touch, because it includes all the organs of the trunk. There must be therefore as many vertebræ in the trunk as there are particular organs placed therein. Of these there are three, the respiratory, digestive, and sexual system, or thorax, abdomen, and pelvis. To the thorax belong the neck, the arms, and the entire set of ribs. 5 vertebræ must appertain to the arms, because they have 5 digits and 5 nerves. But the ribs, and consequently also the digits, are determined by branchial vessels, are only repeated branchial arches, whose number in almost the entire class of fishes is 5. There are therefore also 5 thoracic or pulmonic vertebræ. Since the larynx consists of the 5 original branchial arches, and lies in front of the neck; so must the 5 superior cervical vertebræ stand in the signification of branchial vertebræ. The odontoid process of the second vertebra must be regarded, from its being separated from it in the foetus, as a particular cervical vertebra. Accordingly, in the Thricozoa there are eight cervical vertebræ. The 3 inferior cervical, and the 2 upper costal or rib-vertebræ, give off through their interspaces the nerves of the arms, and are consequently the brachial vertebræ. The 3-7th rib are thus appended to the 5 proper thoracic vertebræ, which stand in the signification of the pulmonary vertebræ. To these succeed the 5 short ribs which belong to the abdomen; their vertebræ are thus intestinal vertebræ. The succeeding vertebræ belong to the sexual system, and are indeed the 5 lumbar or pedal vertebræ, because they furnish the pedal or foot-nerves, the 5 sacral vertebræ being the proper sexual vertebræ. The coccygeal or caudal vertebræ correspond to the cervical vertebræ, and are present for the sake of the sexual branchiæ; usually one and the other is arrested. Thus there are,-- 3×5 Respiratory vertebræ. 3×5 Sexual vertebræ. 1×5 Digestive vertebræ. The number of the sensitive vertebræ is consequently 7×5=35, which are distributed into three groups, in accordance with the principal cavities of the body, whereof the 2 terminal groups consist of 15, but the abdominal group, which combines or unites them, only of 5. The body is accordingly not merely laterally, but also in length, a perfectly symmetrical structure, which has been parcelled out in the following manner into its five stockworks, stories or floors: I. _Dermal vertebra._ A. _Sexual vertebræ._ a. Coccygeal vertebræ 5, b. Sexual vertebræ 5, c. Pedal vertebræ 5.