. Text-book of embryology. Embryology. THE DEFINITIVE VERTEBRA 339 The Composition of the Definitive Vertebra.âA fascinating but difficult chapter in Vertebrate morphology is that which deals with the composition of the definitive vertebra. We have already, in describing the development of the cartilaginous vertebral column, mentioned the elements which go to build it upâneural, haemal, and central. The difficulties, of interpretation arise from the fact that great variety shows itself in the ultimate fate of these elements and in the manner in which they undergo fusion with their neighbours.
. Text-book of embryology. Embryology. THE DEFINITIVE VERTEBRA 339 The Composition of the Definitive Vertebra.âA fascinating but difficult chapter in Vertebrate morphology is that which deals with the composition of the definitive vertebra. We have already, in describing the development of the cartilaginous vertebral column, mentioned the elements which go to build it upâneural, haemal, and central. The difficulties, of interpretation arise from the fact that great variety shows itself in the ultimate fate of these elements and in the manner in which they undergo fusion with their neighbours. This can perhaps best be illustrated by the case of Amia as described â 166.âVariation in vertebral column of Aima. according to Schauinsland (1906). A, tail region of a 7-5 ram. larva ; B, posterior trunk region of an 18 cm. specimen ; C, mid trunk region (18 cm.) ; D, anterior trunk region (18 cm.). Fig. A is more highly magnified than B, C, and D. The position of the boundaries between success- ive myotomes or segments is indicated by the intersegmental blood-vessels (v). A, B, neural arch-elements ; a, 6, haemal arch do.; a, jS, central do. by Schauinsland. Here in some cases two amphicoelous centra (a and fi) are developed corresponding to a single segment, each one carrying its pair of neural and pair of haemal elements, those attached to the anterior centrum {A and a) being relatively small, those on the posterior centrum (B and b) on the other hand well developed. Variations from this diagrammatic arrangement are found in different parts of the body. In the tail region (Fig. 166, A) the original condition frequently persists although in aged individuals the arch-elements (A, a) of the anterior vertebra of the segment are liable to become completely over- grown and hidden by bone. On the other hand there frequently. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearanc
Size: 1727px × 1448px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
