The hypoblastic notochord is early embraced by a mesoblastic sheath derived from the protovertebrae.
Just as the yolk cells of the frog form the ventral wall of the intestine, so nuclei appear along the upper side of the yolk of the fowl, where some protoplasm still exists, and give rise to the ventral hypoblastic cells.
It is hypoblastic in origin and arises in the same way as does the notochord of Amphioxus.
Skeletal structures of epiblastic and hypoblastic origin occur in the Urochordata.
The enamel of the pharyngeal teeth of some Teleosteans is hypoblastic in origin.
The enamel of the pharyngeal teeth of the Salmon and many other Teleosteans is hypoblastic in origin.
These malformations are associated chiefly with imperfect development of the visceral or branchial arches and clefts, or of the hypoblastic diverticula from which the thyreoid and thymus glands are formed.
In the latter he states that the four large cells of the oral face become enclosed by the division and growth of the twelve peripheral cells.
The yolk cells remain distinct on the right side of the body during larval life, and their food material is gradually absorbed for the nutrition of the embryo.
It should be mentioned however that I failed to find a spindle modification of the nuclei in the later stages.
These cells give rise posteriorly to the intestine and anteriorly to the sack, which becomes the stomach and liver.
The larger of these leads into a depression, which may be called the vestibule; and is situated on the posterior side of the oral surface.
It is enclosed in a bivalve shell, the two valves of which meet along the two sides, but are separate along the base.
It flattens out and on its surface is formed the shell, which appears usually to have the form of an unpaired saddle-shaped cuticle, on the two sides of which the valves are subsequently formed by a deposit of calcareous salts.
The epiblastic vesicle now grows rapidly, while the hypoblastic vesicle remains nearly passive and becomes somewhat lens-shaped.
The inner cells next become divided into an hypoblastic layer lining the archenteron, and a mesoblastic layer between this and the now ciliated epiblast.
According to Hatschek it develops as a solid outgrowth of the hypoblastic walls of the mesenteron shortly before the mesenteron joins the oesophagus (fig.
The hypoblastic axes of the tentacles soon lose their connection with the gastric wall.
From these cells an epithelial hypoblastic layer becomes secondarily differentiated, the exact relations of which differ somewhat in the various types.
At about the time of the appearance of the groove the cells become divided into an epiblastic investing layer and a central hypoblastic mass.
The hypoblastic walls of the mesenteron appear to be formed in the first instance laterally (fig.
The two layers of this plate give rise respectively to the epiblast and hypoblast, and at a certain stage the hypoblastic layer ceases to grow, while the growth of the epiblastic layer continues.
Adjoining this thickened layer of epiblast a special thin layer of hypoblast becomes differentiated, which in opposition to the main mass of large nutritive cells forms the true hypoblastic epithelium (fig.
It constitutes the permanent alimentary tract, and is formed of a pharyngeal epiblastic invagination, and a posterior hypoblastic section derived from the primitive archenteron.
It is at first lined by indifferent cells of the lower layer of the blastoderm, which however soon become columnar and form a definite hypoblastic layer (fig.
There are usually only three hypoblastic spheres at the close of the segmentation in the Thecosomata, and a somewhat larger number in the Gymnosomata.
The allantois is without a cavity, but a hypoblastic epithelium is present in the allantoic stalk, through which it does not, however, form a continuous tube.
Calberla states, however, that when the mesoblast is distinctly separated from the hypoblast it does not form a continuous sheet, but two sheets one on each side, between which is placed a ridge of cells continuous with the hypoblastic sheet.
The epiblastic spheres now divide in their turn, giving rise to sixteen spheres which largely enclose the hypoblastic spheres.
Koelliker adduces the fact that the notochord is continuous with the axial cells of the primitive streak as an argument against its hypoblastic origin.
From its origin it may be called the hypoblastic mesoblast, and it is probably equivalent to the hypoblastic mesoblast already described in the chick (pp.
The notochord has sometimes been cited as such an organ, but, as indicated in a previous chapter, it is probable that its hypoblasticorigin can always be demonstrated.
The segmentation cavity thus becomes enclosed between an hypoblastic floor and an epiblastic roof several cells deep.
The larger sphere and its products will be spoken of as the epiblastic spheres, and the smaller one and its products as the hypoblastic spheres, in accordance with their different destinations.
It forms at first a simple hypoblastic tube extending from near the front end of the body, where it terminates blindly, to the hinder extremity where it is united with the neural tube by the neurenteric canal (fig.
Homologous probably with the hepatic cells, and equally of hypoblastic origin, are the spheroidal 'secreting cells' of the pancreas and other glands.
This dilatation becomes the hypoblasticsection of the cloaca.
To the inner side of one wall of this vesicle is attached a mass of granular cells similar to the hypoblastic mass in the blastodermic vesicle of the rabbit.
Both in front and behind, the lateral parts of the hypoblastic sheet become separated from the true alimentary tract as soon as the lumen of the latter is established.
From the above account it follows that the glandular part of the pancreas, and not merely its duct, is derived from the original hypoblastic outgrowth from the gut.
It would not be unreasonable to conclude from this that the compartments were destined to form the hepatic caeca, each caecum being enclosed in a layer of splanchnic mesoblast, and its hypoblastic wall being derived from the yolk cells.
The same figure also shews that the hypoblastic sheet becomes somewhat thicker behind, and more independent of the parts above.
In front, the hypoblastic sheet remains perfectly flat during the formation of the throat, and thus the lumen of the latter has merely the form of a slit.
Somewhat later, the hypoblastic cloaca becomes split into two sections, the hinder one receiving the coalesced segmental ducts, and the anterior remaining continuous with the alimentary tract.
Schenk has thrown doubts upon thehypoblastic nature of the secreting tissue of the liver, but it does not appear to me, from my own investigations, that this point is open to question.
Were it not for the evidence in other types of its being derived from the epiblast we should be inclined to regard it as hypoblastic in origin.
In the gill-slits of Torpedo I have observed a very slight ingrowth of the external skin towards the hypoblastic outgrowth in one single case.
These are derivatives of the hypoblastic cells of the larger ducts and may from the beginning be hollow, possessing a lumen continuous with that of the parent duct (Selachians, Amphibians).
This primary arrangement of the gland, being formed of two main collections of budding hypoblastic cells, corresponds to the adult system of the pancreatic excretory ducts.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "hypoblastic" in a variety of sentences. We hope that you will now be able to make sentences using this word.
