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injected vessels; and the width of the individual meshes of the capillary network may be clearly seen. The section has been carried transversely through the corpus striatum, and at certain intervals large, roundish spots may be distinguished, which appear dark by transmitted light (Fig. 29, a, a, a), but by reflected light and to the naked eye look white, and are formed by transverse sections of the nervous fibres which run in long strands towards the spinal marrow. The vessels scarcely penetrate into them. The rest of the mass, on the other hand, consists of the proper grey substance of the corpus striatum, within which a vascular network with very fine meshes is distributed, the grey substance of the nervous centres being everywhere, both in their interior and in their cortical substance, distinguished from the white by its greater vascularity. A few large vessels are observable in the object, giving off branches, the ramifications of which continually diminish in size, until at last they terminate in capillary networks with very fine meshes. Still, however close this network may be, every element of the substance of the brain by no means comes into immediate contact with a capillary vessel.

The third object is a very slightly magnified injected

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another by transverse anastomoses, and splitting up into

Fig. 30. Injected preparation from the muscular coat of the stomach of a rabbit, magnified eleven diameters.

VESSELS IN CARTILAGE.

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smaller and smaller vessels, which form fine networks within the tissue, so that the whole of it is by this means mapped out into a series of irregularly four-sided divisions. To each of the ultimate intervascular spaces is allotted a certain number of muscular elements, so that the vessels are in some parts in contact with the muscular fibres, whilst in others they lie at a greater distance from them.

If we go on in this way examining the structure of the different organs and tissues, we pass from such as, when injected, seem to consist almost entirely of vessels, in time to those which contain scarcely any, and at last to such as really have none at all. This is most strikingly the case with the connective tissues, and the most important amongst these are bone and cartilage. Perfectly developed cartilage has no longer any vessels at all; perfectly developed bone certainly contains vessels, but in a very variable degree. That perfectly developed cartilage contains no vessels, you will not, I suppose, call upon me to convince you by any additional, special proofs, inasmuch as you have seen various preparations of cartilage, in which not a trace of them was to be observed. (Figs. 6, 9, 22.) I now place before you a piece of young cartilage, because you can see in it what the arrangement of the vessels in cartilage is at an earlier period. It is a section from the calcaneum of a new-born child, and in it the vessels run up from the already-formed central osseous mass into the cartilage which still remains. The preparation shews along the outermost surface of the cartilage the transition from it into the perichondrium, whilst the lower part of the section is taken from the border of the already-formed bone. From this part large vessels are seen running up and terminating in the middle of the cartilage by the formation of loops and plexuses, as it were a tree of villi (Zottenbaum) in the cartilage, and very much resembling a villus of the chorion of the ovum. In fact, the vessels mount up into the cartilage from the

nutrient artery of the bone, but only to a certain height. There they form real loops, and at length break up into a

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fine plexus of capillaries, out of which veins are ultimately formed, and run out again pretty near the spot where the artery entered. But the whole of the rest of the mass consists of non-vascular cartilage, the corpuscles of which, with a low power, look like fine points. Thus there is a whole host of cartilage-corpuscles lying between the terminal loops and the external surface, and the whole of this layer is therefore dependent for its nutrition upon the juice which exudes from the terminal loops and permeates the tissue, though to a trifling extent also upon the materials which the scanty vessels of the perichondrium

Fig. 31. Section of cartilage from the calcaneum of a new-born child. C. The cartilage, with its cells indicated by fine points. P. Perichondrium and adjoining fibrous tissue. a. Inferior border very near to the line of junction between the cartilage and the bone, with the vascular loops ascending from the nutrient artery. b, b. Vessels which make their way through the perichondrium in the direction of the cartilage. 11 diameters.

VESSELS OF BONE.

BONE-CORPUSCLES.

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convey to it. The vessels which spring from the nutrient artery mark in all bones, at a tolerably early period, pretty exactly the limits to which the ossification subsequently proceeds, whilst the remnants of the cartilage which remain bordering upon the joint never contain vessels.

With regard to the bones themselves, the disposition of their blood-vessels is in itself tolerably simple, but at the

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same time very characteristic. If we examine the compact substance, we can usually, even with the naked eye, distinguish upon its surface small openings through which vessels enter from the periosteum. With a moderately high power we discover that these vessels (Fig. 32, a) immediately beneath the surface form a network with somewhat long meshes, or a series of tubes anastomosing with one another

Fig. 32. Longitudinal section from the cortex of a sclerotic tibia. a, a. Medullary (vascular [Haversian]) canals, between them the bone-corpuscles for the most part parallel; but at b (in transverse section) concentrically arranged. 80 diameters.

and, generally speaking, running longitudinally, for though they sometimes take a somewhat more oblique course inwardly, they still essentially maintain a longitudinal direction. Between these meshes there remain comparatively wide interspaces, within which, precisely as we before saw the cartilage cells, we here see the bone-corpuscles, and indeed also in a longitudinal direction, parallel to the surface. If the same part be examined in transverse section, we of course see, where the longitudinal canals were previously observed, nothing but their transverse sections here and there united by oblique communications. Between them lies the proper osseous tissue, deposited in lamellar layers, some of them parallel to the surface, some concentrically arranged around the vessels. In the deeper layers of the compact substance this concentric arrangement around the vessels constantly prevails.

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Between these more lamellated parts is left a small quantity of osseous substance (Fig. 33, i) which does not

Fig. 33. Section of bone. a. Transverse section of medullary (vascular [Haversian]) canal, around which the concentric lamellæ, l, lie with bone-corpuscles and anastomosing canaliculi. . Lamellæ divided longitudinally and parallel. . Irregular arrangement in the oldest layers of bone. v. Vascular canal. 280 diameters.

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