which a series of smaller and larger divisions (bundles, fasciculi) are offered to the view. On magnifying the object, an internal arrangement is shown almost exactly corresponding to that which we have observed in the semi-lunar cartilages. Externally, the tendon is invested in its whole circumference by a fibrous mass, in which the vessels are contained, that are entwiped around the tendon. From these at different points vessels proceed into the interior, where they are to be seen in the larger partitions which separate the fasciculi (Fig. 37, a); but into the interior of the fasciculi themselves no trace of a vessel enters, any more than it does into the interior of the semi-lunar cartilages; there, on the contrary, we again meet with the network of cells we have been talking about, or, in other words, the peculiar system of juice-conveying canals of which we lately considered the import in bone.

Tendons may therefore in the first place be divided into larger (primary) bundles, and these in their turn into a certain number of smaller (secondary) fasciculi, which are separated by broadish bands of a fibrous substance containing vessels and fibre-cells, so that a transverse section of a tendon presents a meshed appearance. From this intervening substance, which must not, however, be regarded as a tissue of a peculiar description, there pass into the interior of the fasciculi stellate cells (tendon-corpuscles) which anastomose with another and establish a communication between the external vascular, and the internal non-vascular, parts of the fasciculi. This relation is, of course, much more evident in the tendons of children than in those of adults. The older the parts become, namely, the larger and finer do the processes of the cells in general become, so that in many sections we do not meet with the real bodies of the cells, but only see minute specks, which, by altering the focus, may be traced into filaments or point-like orifices. The individual cells, therefore, come to be more widely

separated, and it becomes more and more difficult to obtain a view of the whole of a cell at once. Besides, we must first obtain a clear notion of the relation between a longitudinal

FIG. 38.

and a transverse section. Where, namely, in a longitudinal section, there are spindle-shaped cells, in a transverse section will be seen stellate ones, and to the network of cells displayed in the transverse section corresponds the regular succession of spindle-shaped corpuscles, arranged in rows which we see in a longitudinal section, entirely in correspondence with the plan which we have shown to be followed in connective tissue. The cells, therefore, are here also only apparently simply spindle-shaped, when an exactly longitudinal section is examined; but if it has been made a little obliquely, the lateral processes are perceived, by

Fig. 38. Transverse section from the interior of the tendo Achillis of a new-born child. a. The intervening mass which separates the secondary fasciculi (corresponding to Fig. 37, c), and entirely composed of densely aggregated spindle-shaped cells. Directly anastomosing with these, we see on both sides at b, b, reticulating and spindle-shaped cells running into the interior of the fasciculi. 300 diameters.

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THEIR NUTRITION.

93

means of which the cells of one row communicate with those of another.

Up to the present moment the progress of the growth of tendons after birth has not been made the subject of a regular investigation, and it is unknown whether any further multiplication of the cells takes place in them; this much, however, is certain, that the cells in many places afterwards become much elongated, and the intervals between the individual nuclei extremely great. The actual structural relations, however, do not thereby experience any change; the original cells also continue members of the great system of tubes, which in the perfectly developed tendon pervades the whole tissue. Hence we see how,

Fig. 39. Longitudinal section from the interior of the tendo Achillis of a new-born child. a, a, a. Intervening bands. b, b. Fasciculi. In both we see spindle-shaped, nucleated cells, partially anastomosing, with an inter-cellular substance slightly striated in a longitudinal direction, the cells being more crowded in the bands, and less numerous in the fasciculi.. c. Section of an interstitial blood-vessel. 250 diameters.

although the tendon contains no vessels in its most internal parts, and, as may be observed in every case of tenotomy, receives but little blood by the external vessels of its sheath, and by the internal vessels of the septa between the larger fasciculi, it is possible, notwithstanding, for a uniform nutrition of the parts to take place. This we cannot imagine to be effected in any other way than by the distribution of nutritive juices in a regular manner throughout the entire substance of the tendon by means of special canals distinguishable from the vessels. The natural divisions of the tendon are, however, nearly entirely symmetrical, so that an equally large quantity of intercellular substance falls to the share of every cellular element, and as the cell-networks in the interior can be directly traced into the dense bundles of cells of the septa, and these in their turn up to the vessels (Figs. 37, 38), we may, I think, unhesitatingly regard these reticulating cells as the channels for the transmission of this intermediate current of nutritive juice, which has no communication by means of orifices with the general circulation.

You have here a fresh instance in support of my view with regard to cell-territories. I would parcel out the whole tendon, not into primary and secondary fasciculi, but rather into certain series of cells connected in a retiform manner; to each series, moreover, I would assign a certain district of tissue, so that in a longitudinal section, for example, about half of each band of basis-substance would belong to one, the other half to another series of cells. What is, therefore, regarded as constituting the proper fasciculi of the tendon would, according to this view, have really to be split up, and the tendon portioned out into a great number of nutritive districts (Ernährungs-Territorien).

This is the condition which we everywhere find recurring in these tissues, and upon it will at the same time be found to depend, as I hope you will convince yourselves by direct observation, the size of the districts invaded by

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UMBILICAL CORD.

95

disease; every disease which essentially depends upon a disturbance in the internal disposition of the tissues is always made up of the sum of the separate changes occurring in such territories. But at the same time the pictures which are here offered to us afford a really æsthetical enjoyment through the delicacy of this arrangement, and I cannot deny that, as often as I look at a section of tendon, it is with a peculiar feeling of satisfaction that I contemplate these reticular arrangements, which effect a union between the exterior and the interior, and, excepting in bone, can in no structure be demonstrated with greater distinctness and clearness than in tendons.

Considering the structure of the cornea and the disposition of its parts, it would be most convenient, gentlemen, to proceed at once to the consideration of its history, still I prefer reverting to it hereafter, inasmuch as it is at the same time the most suitable object for the demonstration of pathological changes. I will therefore only observe here, that in the same way that tendons have their peripheral system of vessels, and that their internal parts are nourished by a delicate juice-conveying system of tubes, so also in the cornea only the most minute vessels extend a few lines over its border, so that the central parts are completely destitute of vessels, as indeed they were obliged to be, in order to allow of the transparency of the tissue.

I should like, on the other hand, in connection with the foregoing tissues, to speak of one which has generally met with but little special preference in histology, but is perhaps more likely to have some interest in your eyes, I mean the umbilical cord. Its substance (the so-called jelly (gelatina) of Wharton*) is also formed by one of those tissues which certainly contain vessels, but yet really possess none. The vessels which are transmitted

Lymphæductus, vel gelatina, quæ eorum vices gerit, alterum succum albumini ovorum similiorem abducit (a placenta) ad funiculum umbilicalem. (Thom. Whart. Adenographia, Amstelodami, 1659, p. 233.)