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A central strand of xylem occupied up to a third of the diameter of the stem. In the lower parts of main stems it was circular, enlarging before it divided prior to dichotomous branching. Higher up it became elliptical in cross-section, corresponding to the two rows of fertile branching units.
Psilotum is a genus of fern-like vascular plants.It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being Tmesipteris.Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales.
The general characterizing feature of the dental morphology of humans are the lack of facial prognathism, a parabola-shaped mandible and maxilla, and molars that are the same size as the front teeth. Humans also have small crowns in relation to body mass and tend to show a reduction in cusp and root number. [ 8 ]
In humans, the molar teeth have either four or five cusps. Adult humans have 12 molars, in four groups of three at the back of the mouth. The third, rearmost molar in each group is called a wisdom tooth. It is the last tooth to appear, breaking through the front of the gum at about the age of 20, although this varies among individuals and ...
Psilotum nudum, the whisk fern, [3] is a fernlike plant. Like the other species in the order Psilotales, it lacks roots. [4]Its name, Psilotum nudum, means "bare naked" in Latin, because it lacks (or seems to lack) most of the organs of typical vascular plants, as a result of evolutionary reduction.
The Foramen cecum, in dental anthropology, is a minor expression of the protostylid of the tooth. It is thus indirectly related to the five non-metric dental crown traits. According to dental, biological studies, racially mixed populations have been discovered with deformed Foramen cecums, resulting in unique tooth groove patterns. [ 1 ]
Strongly folded tooth surface, involving infolding of the dentin and enamel of the teeth. The cross section resembles a classical labyrinth (or maze), hence the name of the group. [2] Massive skull roof, with openings only for the nostrils, eyes and a parietal eye, similar to the structure of the "anapsid" reptiles. With the exception of the ...
Movement of teeth is determined by two factors: deposition of bone on the tension side and resorption of the bone on the compression side of the periodontal ligament (PDL). During this movement, bone remodelling is initiated by the PDL in which forces are transmitted from the tooth to the alveolar bone. Fibroblasts of the PDL will react to ...