Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: June 4, 2025
The vast division of the Craniota embraces all the Vertebrates known to us, with the exception of the Amphioxus. All of them have a head clearly differentiated from the trunk, and a skull enclosing a brain. The brain is very rudimentary at first, a mere bulbous enlargement of the fore end of the medullary tube.
You know women, young 'confrere'. To calm this impatience, I spontaneously proposed a consultation, and naturally pronounced your name, which is well known by your fine work on the medullary lesions. I supported it, as was proper, with the esteem that it has acquired, and I have the satisfaction to see it accepted."
Long before there is any trace of the skull, limbs, etc., in the embryo of man or any of the higher Vertebrates at the early stage in which the whole body is merely a sole-shaped embryonic shield there appears in the middle line of the shield, directly under the medullary furrow, the simple chorda.
As the reader will remember, the straight medullary furrow first appears in the middle of the sandal-shaped embryonic shield. At each side of it the parallel borders curve over in the form of dorsal or medullary swellings.
They resemble tadpoles in outward appearance, and use their tails as oars, as the tadpoles do. However, this lively and highly-developed condition does not last long. At first there is a progressive development; the foremost part of the medullary tube enlarges into a brain, and inside this two single sense-organs are developed, a dorsal auditory vesicle and a ventral eye.
Two nerve fibers, showing the nodes or constrictions of Ranvier and the axis cylinder. The medullary sheath has been dissolved away. The Nervous System Compared to a Telegraphic System. In men and other highly organized animals, nerves are found in nearly every tissue and organ of the body.
The consistence of the tumour depends on the nature and amount of the stroma, and on the presence of degenerative changes. The softer medullary forms are composed almost exclusively of cells; while the harder forms such as the fibro-, chondro-, and osteo-sarcoma are provided with an abundant stroma and are relatively poor in cells.
There is also much silicified wood, both common dicotyledonous and coniferous: a section of one specimen in the direction of the medullary rays has, as I am informed by Mr. R. Brown, the discs in a double row placed alternately, and not opposite as in the true Araucaria.
In proportion to his bulk, the weight of his brain far exceeds that of any other quadruped the very smallest animals alone being excepted, in whom there must be a certain accumulation of medullary matter in order to give origin to the nerves of every system, as numerous in the minutest as in him of greatest bulk.
It is important to note that some of these gigantic lycopods, which are classed with the CRYPTOGAMS, or flowerless plants, had pith and medullary rays dividing their cylinders into woody wedges. These characters connect them with the PHANEROGAMS, or flowering plants. Like so many of the organisms of the remote past, they were connecting types from which groups now widely separated have diverged.
Word Of The Day
Others Looking