. Chordate morphology. Morphology (Animals); Chordata. vascular pulp canal Figure 8-27. A, section of the armor of a Middle Devonian arthro- dire, ro//icht/iys po/oris, which lacks the basal laminated component; B, enlargement of section through a denticle to show the semidentine and unipolar cell lacunae. (After Bystrow, \9S7\ cled part, a spongy middle zone, and a laminated base. There are numerous canals for Sharpey's fibers. In forms without enamel and with several generations of semidentine tuber- cles, Sharpey's fibers penetrate the upper layers of the armor as well. The ontogeny and phy
. Chordate morphology. Morphology (Animals); Chordata. vascular pulp canal Figure 8-27. A, section of the armor of a Middle Devonian arthro- dire, ro//icht/iys po/oris, which lacks the basal laminated component; B, enlargement of section through a denticle to show the semidentine and unipolar cell lacunae. (After Bystrow, \9S7\ cled part, a spongy middle zone, and a laminated base. There are numerous canals for Sharpey's fibers. In forms without enamel and with several generations of semidentine tuber- cles, Sharpey's fibers penetrate the upper layers of the armor as well. The ontogeny and phylogeny of the scales of arthrodires has been described as follows. The earliest form had rela- tively thin armor consisting of a spongy bone, covered with numerous denticles. The denticles had sharp tops and ridges directed anteroposteriorly. It is quite possible that the pulp cavities of these denticles were rather large. In the later forms the armor was thicker but still without the basal laminar portion, and the pulp cavities of the denticles had become largely filled with prodentine osteons. In the next stage, the dentine of the denticles was re- placed by semidentine and new layers of denticles were formed over the old. In the late forms the laminar basal part of the armor had been added, the denticles were reduced in size, the amount of enamel covering them was decreased. Several generations of tubercles were formed and over- grown by bone. The spongy layer of bone underwent ex- tensive reorganization and increased in thickness as the plate was added to both to its outer and inner surface. In the most advanced forms only the semidentine remnants of the tubercles remained, associated with prodentine, and several generations of these were deeply embedded in the bony outer surface of the plate. The bony plate was now thick and had a well-developed laminar base (isopedine). Anfiorch The plates oi Bothriolepis (Figure 8-28) are quite like those of the euarthrodire; the outer s
Size: 1775px × 1407px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
