. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. SKELETON. 47 to the sheath of the notochord. In what must be considered the most primitive condition the arches extend no further than the sheath and nothing comparable to a centrum is found, even when ossification occurs. In the formation of centra two methods of extension of cartilage to the chordal region are known. In the elasmo- branchs immigrating cells from the arches break through the elastica externa and distribute themselves through the sheath, converting it into cartilages. In other vertebrates (fig.
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. SKELETON. 47 to the sheath of the notochord. In what must be considered the most primitive condition the arches extend no further than the sheath and nothing comparable to a centrum is found, even when ossification occurs. In the formation of centra two methods of extension of cartilage to the chordal region are known. In the elasmo- branchs immigrating cells from the arches break through the elastica externa and distribute themselves through the sheath, converting it into cartilages. In other vertebrates (fig. 43) the immigrating cells extend around the elastica externa so that the sheath eventually comes to lie inside the centrum. In many fishes and fossil amphibians another element, the intercalare, enters into the composition of the neural arch on either " side. The intercalaria lie above and behind FIG 4I _Trunk vertebne the neurapophyses and may expand dorsally of Kkynchobatus, after Durne- , , ' i ril. h, haemal process; i, in- so that the arch is completed by them above. tercaiary piate; ;/, ligament; The dorsal root of the spinal nerve usually n>.neural process; r, rib; s, spmous process. passes through the intercalare, the ventral through the neurapophysis, but both roots may pass between them. Similar intercalaria may occur in the haemal arch. In the trunk region there may be separate elements of the centra; in each somite a trans- verse cartilage (hypocentrum) across the under side of the neural sheath, and a pleurocentrum on either side, behind the hypocentrum (fig. 42).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. Philadelphia, P. Blakiston's son & co.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
