| OCR Text |
Show 1899.] OSTEOLOGY OF THE PYGOPODES. 1033 iv. THE VERTEBRAL COLUMN. The vertebrae seem to resemble those of the Steganopodes more nearly than of any other group, aud, amongst the Steganopodes, they most nearly approach those of Phalacrocorax. They are quite different from those ot: the Impennes or Tubinares. They can, however, be at once distinguished from those of Phalacrocorax, in that the thoracic vertebrae are heteroccelous ; but they differ also in other respects. The odontoid ligament of the atlas is not ossified. The neural arches of the anterior cervicals are not, like those of the Impennes and Tubinares, deeply notched posteriorly. In the Colymbi they are sharply truncated and very broad, in the Podicipides they are, as in Phalacrocorax, marke I by a slight notch; this notch, however, is cut out of the coalesced bases of a pair of hyperapophyses and lies behind the postzygapophyses; ordinarily such a notch is formed by cutting away the neural arch itself so as to leave the postzygapophyses as a pair of articular surfaces, each at the termination of a A-shaped fork. The hyperapophyses of these vertebrae in the Divers take the form of stout pillars, grooved at the top. In the Grebes the pillars become mere tubercles placed close together and deeply grooved superiorly. In this they resemble the vertebrae in the same region of Phalacrocorax. The neural arches of the posterior cervicals do not present any very noticeable features. In the Colymbi the 5th to the 10th vertebrae bear catapophyses, which, rapidly converging, give place to hypapophyses. These run backwards to the extreme end of the centrum in the form of a strong median keel. The vertebrae 1-4and 11-13 bear catapophyses. In the Podicipides the cervical catapophyses from the 3rd to 13th vertebrae form deep tubular grooves for the carotids, recalling those of Plotus and Phalacrocorax. The cervicals 1-3 and 16-23 bear well-developed hypapophyses. Tbe thoracic vertebrae-and the last cervical-in the Divers are all free, save the last, which is anchylosed with the synsacrum. 1 to 5 bear median hypapophyses, with broadly expanded free ends, as in Alcidae and some Impennes, e. g. Pggoscelis. In the Grebes the last cervical and the thoracics 1-4 are anchylosed to form one mass ; the 5th thoracic is free, but the 6th and 7th are fused with the synsacrum. The synsacrum of the Pygopodes is remarkable for the extraordinary lateral compression which it has undergone, accompanied by an almost complete suppression of the di- and parapophysial elements. Pleurosteal elements appear to be wanting. Prom the evidence obtainable from the synsacral region of a nestling Grebe we may perhaps be justified in holding that the synsacrum of the adult includes some 15 to 17 vertebrae. Of these the 1st is thoracic, the next 4 are lumbar, then follow 3 lumbo-sacral, 2 sacral, and 5 or 6 caudal. The 3rd aud 4th lumbar bear small nipple-like parapophysial processes at the base of the neuron,behind these follow, as just stated, 3 lumbo-sacral and 2 sacral. |
