through the umbilical cord, do not immediately contribute to its nourishment, at least not in the sense in which we speak of nutrient vessels in other parts. For when we speak of nutrient vessels, we always mean vessels which have capillaries in the parts which are to be nourished. The thoracic aorta is not the nutrient vessel of the thorax, any more than the abdominal aorta, or the vena cava, is that of the abdominal viscera. We should expect, therefore, in the case of the umbilical cord to find umbilical capillaries in addition to the two umbilical arteries and the umbilical vein. But these arteries and this vein run their course to the placenta, without giving off a single small vessel, and it is only when they have reached that body that they begin to ramify. The only capillary vessels which are found in the whole length of the umbilical cord of a somewhat developed foetus do not extend more than about four or five lines (in rare instances a little farther), beyond the abdominal walls into that part of the

FIG. 40.

cord which remains after birth. The farther up this vascular part extends, the greater the development of the navel. When the vascular layer is prolonged but a very short distance the navel is greatly depressed; when it reaches a long way up, a prominent navel is the result. The capillaries mark the limits of the permanent tissue; the deciduous portion of the cord has no vessels of its own.

This condition, which seems to be of great importance as regards the theory of nutrition, can be very easily seen with

Fig. 40. The abdominal end of the umbilical cord of a nearly full-grown fœtus, injected. 4. The abdominal wall. B. The permanent part of the cord with a congeries of injected vessels along its border. C. Its deciduous portion with the convolutions of the umbilical vessels. v. The limits of the capillaries.

THE UMBILICAL CORD.

97

the naked eye in injected foetuses of five months and upwards, and in new-born children. The vascular layer terminates by a nearly straight line.

Preparations of this sort do not, to be sure, furnish absolute proof, for there might happen to be a few minute vessels proceeding farther up, but invisible to the naked eye. But I formerly made this very point the subject of special investigation, and although I injected a number of umbilical cords, some from the arteries, and others from the veins, I never succeeded in discovering a single collateral vessel, however minute, that passed the limits of the persistent layer. The whole of the deciduous portion of the umbilical cord, that long portion which lies between its cutaneous end and its termination in the placenta, is entirely destitute of capillaries, and there really exist no other vessels in it than the three large trunks. Now these are all of them remarkable for the great thickness of their walls, which, as we have really only known since the investigations of Kölliker, are enormously rich in muscular fibres.

In a transverse section of the umbilical cord it may be observed, that the thick middle coat of the vessels is entirely composed of smooth muscular fibres, lying in immediate contact one with the other, and in such abundance as is scarcely to be seen in any completely developed vessel. This peculiarity explains the extraordinarily great contractility of the umbilical vessels, which can be so readily seen in action on a large scale when mechanical stimuli are applied, when the vessels are divided with scissors or are pinched, or after the employment of electrical stimuli. Sometimes, upon the application of external stimuli, they even contract to such a degree that their canal is entirely closed, and thus after birth, even without the application of a ligature, as when, for example, the umbilical cord has been torn asunder, the bleeding may stop of itself. The thickness of the walls of these vessels is, therefore, easily

comprehensible, for in addition to the muscular coat, which is of itself so thick, there is an internal, and, though it is certainly not very strongly developed, an external, coat; and only after this do we come to the gelatinous, jelly-like tissue (mucous tissue (Schleimgewebe)) of the umbilical cord. Through these layers, therefore, nutrition would have to take place, if the umbilical vessels were the nutrient vessels of the cord. Now I certainly cannot say with certainty whence the tissue of the umbilical cord derives its nourish

ment; perhaps it receives nutritive matter from the liquor amnii, nor am I inclined to deny the possibility of nutriment's passing through the walls of the vessels, or of the onward conveyance of nutritive materials from the small capillaries of the persistent portion. In any case, however, a large extent of tissue lies at a distance from all vessels and from the surface, and is nourished and supported without the presence of any minute system of blood-vessels in it.

Fig. 41. Transverse section through a part of the umbilical cord. On the left is seen the section of an umbilical artery, with a very thick muscular coat, and to this, as one proceeds outwards, succeeds the gradually widening network of cells of the mucous tissue of the cord. 80 diameters.

THE MUCOUS TISSUE OF THE UMBILICAL CORD. 99

For a long space of time, indeed, no one troubled himself any further about this tissue, because it was designated by the name of jelly, and thereby summarily ejected from the number of the tissues and thrust into the ambiguous group of mere accumulations of organic materials. I was the first to show that it is really a well-constructed tissue of a typical form, and that what constitutes the jelly in the more restricted sense of the term, is the expressible part of the intercellular substance, after the removal of which there remains a tissue containing a delicate network of anastomosing cellular elements, similar to that which we have seen to exist in tendons and other parts. A section through the external layers of the umbilical cord exhibits a structure bearing great resemblance to the external layers of the cornea; first, an epidermoidal stratum, beneath it a somewhat denser dermoid layer, and then the Whartonian jelly, which corresponds in texture to the subcutaneous cellular tissue, and is in some sort equivalent to it. This has a peculiarly interesting bearing upon the tissues of a more advanced period, inasmuch as, by thus ranking the jelly with subcutaneous tissue, we at the same time establish its very close relationship to the vitreous body, which is the only remnant of tissue that, as far as I have until now been able to make out, persists in man in this condition of jelly. It is the last remnant of the embryonic subcutaneous tissue which in the development of the eye is inverted with the lens (which was originally epidermis, p. 38).

The proper substance of the umbilical cord consists of a reticulated tissue, the meshes of which contain mucus (mucin) and a few roundish cells, whilst its trabeculæ are composed of a striated fibrous substance. In this lie stellate corpuscles, and when a good preparation has been obtained by treatment with acetic acid, a symmetrical network of cells is brought to view, which splits up the mass into such regular divisions, that by means of the

anastomoses which subsist between these cells throughout the whole of the umbilical cord, a uniform distribution of

I have up to the present time, gentlemen, brought to your notice a series of tissues all of which agree in containing either very few capillary vessels, or none at all. In all these cases the conclusion to be drawn seems to be very simplethat, namely, the peculiar cellular, canalicular arrangement which they possess serves for the circulation of juices. It might, however, be supposed that this was an exceptional property, appertaining only to the non- or scantily-vascular and, generally speaking, hard, parts, and I must therefore add a few words concerning the soft textures which possess a similar structure. All the tissues which we have hitherto

Fig. 42. Transverse section of the mucous tissue of the umbilical cord, exhibiting the network formed by the stellate corpuscles, after the application of acetic acid and glycerine. 300 diameters.