. Elements of comparative anatomy. Anatomy, Comparative. 130 COMPARATIVE ANATOMY. Chimaerae special cartilages are intercalated, which aid the superior arches, which are connected with the bodies of the vertebrae, in closing1 the vertebral canal. In the skeletogenous sheath forms a considerable tube, and the separation of the column into vertebras is only indicated by the superjacent arches. The vertebral column of the other Ganoidei is sharply marked off from this, its lowest form. Amia resembles the Teleostei. A small portion of cartilage is retained at the point where the arch
. Elements of comparative anatomy. Anatomy, Comparative. 130 COMPARATIVE ANATOMY. Chimaerae special cartilages are intercalated, which aid the superior arches, which are connected with the bodies of the vertebrae, in closing1 the vertebral canal. In the skeletogenous sheath forms a considerable tube, and the separation of the column into vertebras is only indicated by the superjacent arches. The vertebral column of the other Ganoidei is sharply marked off from this, its lowest form. Amia resembles the Teleostei. A small portion of cartilage is retained at the point where the arches are connected with the centra of the vertebras; but this is absent in Polypterus, so that in it the arches and the centra are united together by bone. Lepidosteus is the most divergent form, for in it the cartilage becomes constricted between the vertebras. In the cartilage which forms the constrictions, an intervertebral articular cavity is formed, so that the opisthoccelous vertebras articulate with one another. So far they resemble the Amphibia, but, later on, the remnant of the vertebral por- tion of the notochord disappears, and a bony centrum is developed, which is connected, and continuous, with the upper arches. The vertebral column of the Teleostei is cha- racterised by the reduction of the cartilaginous rudiment. This reduction may be seen to be gradual, and may indeed be seen in one and the same vertebral column in certain stages of de- velopment ; where, that is, the cartilage may be seen to diminish in quantity as we go from before backwards. As a rule, four cartilaginous pieces, belonging to the superior and inferior arches (Fig. 221 b, hh1), may be seen around the chord, and these take a certain share in the formation of the arches. They very rarely form complete superior arches. When osseous substance is developed, these cartilages are generally retained in the middle of the centrum, so that on making a vertical section through it we get an obliquely set cros
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
