| OCR Text |
Show 278 ON THE AXIAL SKELETON OF THE URODELA. [APR. 28, DORSAL VERTEBRAE. The vertebrae interposed between the cervical vertebra and the sacrum vary in number from twelve (Taricha) to sixty-three (^w*- phiuma). They are always the largest vertebrae of any one individual axial skeleton. All have neural arches and anterior and posterior zygapophyses. Except in Siren, Proteus, and Amphiuma, all these vertebrae support a transverse process and a rib on each side of the body. Some few forms have small hypapophysial processes (e: g. Spelerpes), or single median ridges, or such ridge more or less cleft longitudinally. The various parts and processes of the vertebrae have been already described. SACRAL VERTEBRA. Never more than one vertebra is normally connected with the hip-girdle; but not very unfrequently the ilium of one side is connected with the transverse process of one vertebra, while the other ilium attaches itself to another vertebra. The transverse process of the sacral vertebra is generally stout, as also the annexed rib. The latter is especially predominant, as compared with the ribs in advance of it, in Axolotl. In Proteus and Amphiuma this vertebra is without a rib. In no genus does it develope a hypapophysial process. CAUDAL VERTEBRAE. These vertebrae always decrease in size successively from before backwards ; the last ones are often merely little bony ossicles without processes of any kind. The number of caudal vertebrae varies from 22 in Cryptobranchus japonicus*, and sometimes in Menobranchus, to about 43 in Amphiuma or 53 in Siren. All except the more posterior ones are provided with neural arches and, with the exception of the first one or two, with hypapophyses. These latter unite to form hypaxial arches in all the species except Siren. Transverse processes are sometimes to be traced for a great distance along the tail, as in Siren, Chioglossa, &c. Sometimes, as in Cryptobranchus and Menopoma, every trace of them disappears at the seventh or eighth caudal vertebra. Sometimes both tubercular and capitular processes stand out distinctly one above another, as occasionally in the fourth vertebra oi Menobranchus (fig. 10, c, t). Small ribs are sometimes attached to the first caudal vertebra, and also to the one or two following ones, as in Menopoma and Cryptobranchus. Anterior and posterior zygapophyses are always developed in the anterior caudals, and continue backwards for a variable, sometimes (e. g. in Amphiuma) for a great extent. But it is here unnecessary to recapitulate details as to the various parts and processes of these vertebrae, which have already been given under the various preceding headings. * In Brit. Mus. |
