All these peripheral nerves grow out of the medullarytube (Figure 1.
At the same time, the neural or medullary tube is formed above the chorda, on the dorsal surface, by the closing of the parallel medullary swellings.
The medullary tube would be originally a chemical sensory organ, a dorsal olfactory tube, taking in respiratory-water and food by the neuroporus in front and conveying them by the neurenteric canal into the primitive gut.
This groove is, of course, the dorsal furrow, and the swellings are the dorsal or medullary swellings; they form the first structure of the central nervous system, the medullary tube.
Under this is a soft medullary substance, which consists of entodermic cells with vacuoles.
This insignificant relic of the medullary tube seems to be quite beyond comparison with the nervous centre of the vertebrate, yet it started from the same structure as the spinal cord of the Amphioxus.
Thus, for instance, the chief part of the central nervous system is a long dorsal neural string that runs above the gut and corresponds to the medullary tube of the Chordonia.
These medullary swellings join together over the furrow, and form a tube; in this case, again, the neural or medullary tube is at first open in front, and connected with the primitive gut behind by the neurenteric canal.
Nevertheless, as we know from human embryology, the medullary tube is formed from the cutaneous layer.
The medullary tube of the Chordonia has been formed by the lengthening of the vertical brain on the dorsal side.
In the earlier stages the alimentary tube is found to be entirely closed, after the closing of the primitive mouth; it only communicates behind by the neurenteric canal with the medullary tube.
The medullary layer, which usually forms the main part of the thallus, is distinguished from the cortical layer by its looser consistence and the presence in it of numerous, large, air-containing spaces.
The medullary folds and notochord are evident at this stage, but no mesoblastic somites are to be seen.
The medullary canal continues for a short distance (about fifteen sections of five microns thickness) posterior to the opening of the neurenteric canal.
There are no medullary rays going out radially through the wood, such as are found in all other zones of secondary wood, and in this arrangement of soft tissue the plants are unique.
The shaft is a cylinder of compact bone enclosing the medullary canal, which is filled with yellow marrow.
Early resection of the shaft is also indicated if the opening of the medullary canal is not followed by relief of symptoms.
Around the cavity the bone is sclerosed, and the medullary canal is obliterated.
The epithelioma originates at the skin orifice of the sinus, and spreads to the bone and into its interior, where the progress of the cancer is resisted by dense bone, which obliterates the medullary canal.
The new bone is laid down on the surface, in the Haversian canals, or in the cancellous spaces and medullary canal, or in all three situations.
The extent of spread in the medullary canal and beneath the periosteum is in close correspondence.
When the sequestrum involves an articular surface it is often wedge-shaped; in other situations it is rounded or truncated and lies in the long axis of the medullarycanal (Fig.
The bones show a feeble shadow with the X-rays, and appear thin and atrophied; the medullary canal is increased at the expense of the cortex.
In long-standing cases it is common to find extensive obliteration of themedullary canal, and a considerable increase in the girth of the bone.
The process may remain localised to the ossifying junction, but usually spreads along the medullary canal for a varying distance, and also extends to the periosteum by way of the enlarged Haversian canals.
When the new bone is laid down in the Haversian canals, cancellous spaces and medulla, the bone becomes denser and heavier, and is said to be sclerosed; in extreme instances this may result in obliteration of the medullary canal.
This is the sago-tree* of the country (* The nutritious fecula or medullary flour of the sago-trees is found principally in a group of palms which M.
Malignant medullary formations occasionally form here, causing most distressing symptoms; by displacing the bowel they may obstruct its canal, and simulate stricture or schirro-contraction.
There is an increased vascularity of the medullary membrane, and the cancellated texture contains thin brownish-looking fluid instead of marrow.
Sometimes it is attacked by, or involved in, medullary sarcoma; and bloody tumours are also met with.
If there be extensive disease in the medullary canal of a bone, several perforations may require to be made, and these may be connected by the use of a small saw, or the cutting forceps.
The nipped surface is liable to exfoliation, or the medullary web is apt to be injured, and this is inevitably followed by more or less death of bone.
The ulna to near the wrist was swollen enormously by purulent collections in its medullary canal.
The portion of outer osseous shell projecting into the medullary canal would in the end have been removed by the absorbents, and the deformity much diminished.
New bone is also furnished from the medullary canal, as is also shown in the sketch.
Not unfrequently the testicle is attacked by swellings of a more serious nature—medullary sarcoma is common, as also both fibrous and soft tumours, with cysts; scirrhus is more rare.
For the medullary substance of the brain not only occupies the cavities of the head and spine, but passes along the innumerable ramifications of the nerves to the various muscles and organs of sense.
The muscular fibres are moving organs intermixed with that medullary substance, which is continued along the nerves, as mentioned above.
It is not absurd to conceive, that the retina may be stimulated into motion, as well as the red and white muscles which form our limbs and vessels; since it consists of fibres, like those, intermixed with its medullary substance.
A nerve is a continuation of the medullary substance of the brain from the head or spine towards the other parts of the body, wrapped in its proper membrane.
The cortical substance ran deep into the medullary part of the brain.
No bloody points were observed in the medullary portion of the brain, when cut.
Below this the inner and outer edge of the provertebral plate splits on each side into two horizontal plates, of which the upper pushes between the chorda and medullary tube, and the lower between the chorda and gastric tube.
The broad ectodermal fold that first appears in the middle line of the flattened dorsal surface, and forms a shallow longitudinal groove, is the beginning of the central nervous system, the medullary tube.
The chordula-embryo of all the vertebrates is characterised by the dorsal medullary tube, the neurenteric canal, which passes at the primitive mouth into the alimentary canal, and the axial chorda between the two.
The oval shield in the centre also looks whitish, and in its axis we see the dark medullary groove.
B In the middle of the germinal disk we find the medullary groove (mr), and underneath it the chorda (ch).
The dorsal half contains the narrow spinal-column cavity or vertebral canal ABOVE the chorda, in which lies the tube-shaped central nervous system, the medullary tube.
On its dorsal side we find in the middle line the straight medullary furrow, bordered by the two parallel dorsal or medullary swellings.
As this ventral groove gradually deepens, and its lower edges bend towards each other, it is formed into a closed tube, the alimentary canal, in the same way as the medullary groove grows into the medullary tube.
Two substances, distinguishable by their color, namely, the white or medullary and the gray or cortical substance, enter into the formation of nervous matter.
In the first they are surrounded by an external bony ring, and the medullary cavity is closed by a bony plug or stopper, constituting the period of the provisional callus.
Sections through the hind end of the medullary groove.
Along the axial line there is placed, as we have stated above, the medullary plate.
By the closing of the groove there is formed the medullary canal above, while the part of the groove on the under surface directed below is chiefly converted into the hind end of the alimentary tract.
The medullary plate is more distinct, and a shallow but unmistakable medullary groove has made its appearance.
The medullary keel, though retaining to a great extent the shape it had in the last stage, is no longer completely solid.
It becomes narrowed as the medullary folds finally unite to form the medullary canal, and eventually disappears.
The passage at the front end of the primitive streak forms the posterior boundary of the medullary plate, though the medullary groove is not at first continued back to it.
C, the medullaryfolds have nearly met above, but have not yet united.
Avian embryo, forming the parietal part of the body; and (2) a central portion consisting of the vertebral and medullary plates and the axial portions of the embryo.
The medullary groove has disappeared, but the medullaryplate (mp.
In the caudal region the medullary folds spread out and enclose between them the blastopore, behind which they soon meet again.
The character of the cortical and medullary cells is nearly the same, and the cells of the two strata appear rather to differ in shape than in any other essential point.
In some trees you will see rays, or lines, radiating from the centre, and known as the medullary rays (Figs.
It shrinks much less in the line of the medullary rays, that is, across the tree.
The more exactly the side of a board is cut on the radial line the more richly the figure of the medullary rays will be shown, as in Fig.
We have seen how a log in drying cracks along the radial lines (page 31), thus showing the natural lines of cleavage or separation in the direction of the medullary rays, that is, radiating from the centre.
We distinguish in the wood of the cactus the medullary prolongations, as M.
They make bread of the medullary flour of this palm-tree, which is the sago of America.
Nevertheless, as the wood is kept in connection with the bark by the medullary rays, many products which probably originate in the former are deposited in the wood.
A small brain usually subbilobed, crowning a knotty double medullary chord; nerves proceeding from the brain and other ganglions to all parts of the body.
A small bilobed brain crowning a double, knotty, medullary chord; nerves proceeding from the brain and other ganglions to all parts of the body.
This central thread is the essential nerve; and the sheath of medullary matter, and its surrounding membranous sheath, are only its accessories.
The white tissue is composed of minute tubes containing a medullary substance or pulp, viscid like oil.
This belongs to the class of small bones, in that it possesses no medullary canal.
The ends of the bones are thus exposed, and their medullary cavities exposed to infection.
The medullary plate is thickened at the two sides, and is grooved in the median line by a delicate furrow (fig.
The mesoblast is represented as having grown in between the medullary canal and the superjacent epiblast.
In the median line of the embryo underneath the medullary groove there are undoubtedly from the first certain cells which eventually give rise to the notochord; and it is these cells the nature of which is in doubt.
In front the medullarycanal ends blindly, but behind it opens freely into the still persisting blastopore, with the lips of which the medullary folds become, as in other types, continuous.
The first traces of it become apparent while the medullary groove is still extremely shallow.
Shortly after the medullary folds have met behind the whole canal becomes closed in.
On the closure of the medullary canal, its walls become separated from the external epiblast, which extends above it as a continuous layer.
Behind its opening the medullarycanal is continued back as a small diverticulum, which follows the course of the primitive groove and is apparently formed by the conversion of this groove into a canal.
In the relation of the medullary canal to the blastopore, as well as in the closure of the medullary groove from behind forwards, the Solitary Ascidians agree closely with Amphioxus.
The medullary rays usually consist of a single tier of cells, but in the Pinus type of wood broader medullary rays also occur and are traversed by horizontal resin-canals.
The secondary wood of the shoot and root conforms in the main to the coniferous type; in the short shoots the greater breadth of the medullary rays in the more internal part of the xylem recalls the cycadean type.
It is of interest to note that the leaves of Gnetum, while typically Dicotyledonous in appearance, possess a Gymnospermous character in the continuous and plate-like medullary rays of their vascular bundles.
Wavy and curly, or smooth and silky, oval in section, withmedullary tube but no pith.
The large medullary rays give to the wood a characteristic parenchymatous or lax appearance, which is in marked contrast to the more compact wood of a conifer.
An anatomical peculiarity in the veins of Pinus and several other genera is the continuity of the medullary rays, which extend as continuous plates from one end of the leaf to the other.
When tracheids occur in the medullary rays of the xylem these are replaced in the phloem-region by irregular parenchymatous cells known as albuminous cells.
These are called the medullary rays, or silver-grain; they form an exterior layer or ring of cellular substance on the outside of the wood, which is called the cambium.
The same people make bread of the medullary flour of this palm, which it yields in great abundance, if cut down just before going to flower.
The fibres descending from the developing buds on the stem, and passing between the plates of cellular tissue, which constitute the medullary rays, and the cells of which have a horizontal direction, are but the basis of the vegetable fabric.
It is said to be produced by the metamorphosis of the medullary rays under unfavorable conditions of growth.
Each lobe is divided into a large number of lobules divided by areolar tissue, and each of these, under the microscope, is seen to consist of a cortical and medullary part.
The medullary part consists of small islets of cells, which resemble columnar epithelium lying among venous sinuses; these cells are said to be in close connexion with the sympathetic nerve filaments from the great solar plexus.
To the naked eye the cortical part is yellow while the medullary is red.
Minot (Human Embryology, 1897) believes that the original cells which grow in from the sympathetic disappear later, and that the adult medullary cells are derived from the cortical.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "medullary" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: pithy; pulpy; spongy
