It shews the deep constriction separating the thalamencephalonfrom the cerebral hemispheres.
The typical Ganoid characters of the thalamencephalon and the cerebral hemispheres (vide pp.
The roof of the thalamencephalon immediately in front of the pineal gland forms a sort of vesicle, the sides of which extend laterally as a pair of lobes, shewn in transverse sections in Plate 37, figs.
The vesicle of the roof of the thalamencephalon is therefore to be regarded as a peculiar development of the tela choroidea of the third ventricle.
The large size of the thalamencephalon is also characteristic of the Ganoid brain in comparison with the brain of the Dipnoi; but is not however so very much more marked in the Ganoids than it is in some Elasmobranchii.
On the whole, we may consider the retention of a large thalamencephalon as a primitive character.
Below, thethalamencephalon is produced into a very elongated infundibulum (Plate 37, figs.
On the roof of the thalamencephalonis placed a large thin-walled vesicle (Plate 38, figs.
In the median line the roof of the thalamencephalon is thin and folded; at its posterior border is placed the opening of the small pineal gland.
The immense length of the region of the thalamencephalon is a feature in the Ganoid brain which must at once strike any one who examines figures of the brains of Chondrostei, Polypterus, or Amia.
The sides of the thalamencephalon are greatly thickened, forming the optic thalami (Plate 37, figs.
They grow rapidly in size, and extend, especially backwards, and gradually cover the thalamencephalon and the mid-brain (fig.
They have thus come to lie in front of the mid-brain, and to form the end of the long axis of the body, and have at the same time compressed the originally largethalamencephalon against the mid-brain.
The sides of the thalamencephalon become very early thickened to form the optic thalami, which constitute the most important section of the thalamencephalon.
To the roof of the thalamencephalon is attached a flattened sack (pn) which is probably the pineal gland.
The thalamencephalon varies so slightly in structure throughout the Vertebrate series that a general description will suffice for all the types.
The proximal extremity attached to the roof of the thalamencephalon forms a special section, known as the infra-pineal process.
The constriction to which the stalk or optic nerve is due takes place obliquely downwards and backwards, so that the optic nerves open into the base of the front part of the thalamencephalon (fig.
The anterior region becomes at an early period excessively thin, and at a later period, when the roof of the thalamencephalon is shortened by the approach of the cerebral hemispheres to the mid-brain, it becomes (vide figs.
In the floor of the thalamencephalon are two masses of ganglionic tissue, the optic thalami.
In the posterior part of the roof of the thalamencephalonis the small posterior commissure (Ahlborn, Zeits.
The optic chiasma, where present, is involved in the floor of the thalamencephalon and forms a large, upwardly-projecting ridge.
The floor of the thalamencephalon projects downwards and backwards as the infundibulum.
The posterior commissure is situated in the boundary between thalamencephalonand mid-brain.
The dorsal sac is formed by that part of the roof of the thalamencephalon lying between the habenular commissure and the region of the velum.
The thalamencephalon is one of the most interesting parts of the brain from its remarkable uniformity throughout the Vertebrata.
These constrictions are in the position of commissural bands of nervous matter; of these the limiting nervous strands between the thalamencephalon and mesencephalon and between the mesencephalon and the hind-brain are of primary importance.
The cerebral hemispheres are not convoluted, and, looked at from the dorsal aspect, do not hide the thalamencephalon and mid-brain.
The fore-brain consists of a thalamencephalon (th.
The typical Ganoid characters of the thalamencephalon and the cerebral hemispheres.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "thalamencephalon" in a variety of sentences. We hope that you will now be able to make sentences using this word.
