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These are the thymus and thyroid glands, apparently vestigial structures. The thymus gland attains a considerable development in the embryo and shrinks away to the merest vestige in the adult. It begins to form early in the embryo life as an epithelial ingrowth from the throat, and extends from the neck into the chest.
As to any power of fascination exercised by means of these actions, the most distinguished naturalists, certainly the most distinguished erpetologists, entirely deny it, and it is opposed to the careful observations of those known to us. The eye is formed by a simultaneous and corresponding ingrowth of one part and outgrowth of another.
In the further course of development the epiblast becomes the ectoderm or epidermic layer of the body; the hypoblast becomes the epithelium of the middle portion of the alimentary canal; and the mesoblast gives rise to all the other tissues, except the central nervous system, which originates from an ingrowth of the epiblast.
But although in the exploit of Mysie Gilmour, and Robin Finnie with his confederates, we had a tasting of mirth and merriment, to the effect of lessening the dread and fear in which our simple country folk held his Majesty's ungracious fine-levers, the cavalier captains and soldiers, still there was a gradual ingrowth of the weight of the oppression, wherewith we were laden more as bondsmen and slaves than as subjects; and, in the meantime, the spirit of that patriarch, my apostolic grandfather, was gathering to heart and energy within the silent recesses of my afflicted bosom.
Within a few hours the peritoneal surfaces are glued together by a thin layer of fibrin and leucocytes, which is speedily organised and replaced by fibrous tissue. Fibrous tissue takes the place of the muscular elements, which are not regenerated. The mucous lining is restored by ingrowth from the margins, and there is evidence that some of the secreting glands may be reproduced.
The histology of ainhum shows it to be a direct ingrowth of epithelium, with a corresponding depression of surface due to a rapid hyperplasia that pushes down and strangles the papillae, thus cutting off the blood supply from the epithelial cells, causing them to undergo a horny change. The disease is not usually symmetric, as formerly stated, nor is it simultaneous in different toes.
It continues to grow after birth, but later begins to shrink and nearly disappears in the adult. The thyroid gland has a somewhat similar origin, it beginning as an ingrowth from the lower section of the pharynx and extending down to the lower part of the neck. It subsequently loses its connection with the pharynx, and in adult life is a bilobed structure on either side of the windpipe.
The skin in front of the future eye becomes depressed, the depression increases and assumes the form of a sac, which changes into the aqueous humour and lens. An outgrowth of brain substance, on the other hand, forms the retina, while a third process is a lateral ingrowth of connective tissue, which afterwards changes into the vitreous humour of the eye.
This granulation tissue is gradually replaced by young cicatricial tissue, and the surface is covered by the ingrowth of epithelium from the edges. This modification of the reparative process can be best studied clinically in a recent wound which has been packed with gauze. When the plug is introduced, the walls of the cavity consist of raw tissue with numerous oozing blood vessels.
If the cancer already covers an extensive area, or has invaded the cavity of the orbit or nose, radium or X-rays yield the best results. The effect is soon shown by the ingrowth of healthy epithelium from the surrounding skin, and at the same time the discharge is lessened.
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