dorsal, roots of the aorta formed by the union of the branchial arches on each side of the intestine.

From the very cold state of the weather at the time I made these observations, I found it very difficult to keep the chick alive on the field of the microscope, and to observe the circulation of the blood going on, at the early stage of advancement necessary in this investigation, and I was obliged to have recourse to the plan of making transverse sections of the foetus in the whole length of its body, in order to ascertain the structure of its vessels, a mode of observation by no means easy, but one which affords most certain and satisfactory results. In this manner, I have been enabled to confirm the general results stated by M. Serres in regard to the double state of the aorta, in the early stages of the development of the foetal bird.

In the chick, at the 36th and at the 40th hours of incubation*, or a little before and immediately after the circulation of the blood commences, I have seen two vessels rising from the bulb of the heart, winding round the anterior portion of the intestine, and continuing to descend along the body of the foetus, parallel to but separate from one another in their whole length. These vessels are situated below the spinal marrow, and on each side of the chorda dorsalis †, or part afterwards occupied. by the bodies of the vertebra. The omphalo-mesenteric arteries are given off from these vessels considerably higher at this than at a later period, and at first sight appear to be the only branches continued from the aortic vessels; but on minute examination, two other smaller vessels may be seen, situated between the omphalo-mesenterics, and descending some little way below the place where these latter arteries pass off into the vascular area: towards the tail of the embryo, these two continuations of the aortic vessels seem to lose themselves in a large vacant space left between the vascular layer of the germinal membrane and the chorda dorsalis.

In the chick at the 48th or 50th hours, or at the period when

In mentioning the hours of incubation, I state the period, not according to the time occupied in the incubation of the individual foetuses employed, but according to the state of their advancement, and the general periods adopted by Baer, Prevost and Dumas, &c.

The Chorda dorsalis, so called by Baer, corresponds in its position to the primitive streak of the cicatricula: it is a small dense cord, situated immediately below the spinal marrow.

JANUARY-MARCH 1831.

T

the circulation of the blood is now completely established on the vascular area, but before the second set of veins have appeared, I have found the two aortic vessels united for a considerable space in the dorsal region. This union seems to commence in the back, nearly opposite to the auricle, but I have not been able to ascertain the precise period at which this process begins: it gradually extends backwards towards the tail, so that, at the 60th or 65th hour, the whole of the dorsal and part of the abdominal aorta is one tube, as far as the place where the omphalomesenteric arteries are given off. The omphalo-mesenteric arteries, being shortly after this partially united, appear to arise from one stem.

On the fourth day, the whole of the two abdominal portions of the aorta becomes united, as far as the region where the permanent division of this vessel takes place: here the vessels remain separate, and furnish the umbilical arteries or vessels of the allantoid membrane, which now begins to be developed,― these being the first considerable branches of the iliac arteries which are formed.

While this union of the dorsal and abdominal portions of the double aorta takes place, the two vessels arising from the bulb of the heart, of which the aortæ formed at first the continuation, do not, like these, become united into one trunk, as the observations of M. Serres would lead us to believe. I have already described these two vessels as the first pair of branchial arches, the posterior parts of which form the separate roots of the aorta to be found in the chick on the third and fourth days of incubation; these roots being also joined at this period by the four other branchial arches which appear successively on each side of the pharynx. These roots of the aorta and branchial arches, we have already remarked, do not become united to one another, but undergo other very remarkable changes, by their partial enlargement or obliteration. Parts of the first branchial arches give rise to the carotid arteries in all vertebrated animals: while the proper trunk of the aorta, or at least its ascending portion and arch, is produced from other branchial vessels, and the roots into which they are joined; one or more of these serving to form the aorta, according to the

* See page 257, &c. and figs. 20, 21, and 30. in the last Plate.

class of animals in which the transformation occurs. In Mammalia, the aorta is formed by the permanence of the fourth branchial arch and the aortic root of the left side; in Birds by that on the right; in the greater number of Reptiles by one on each side; in the tailed Batrachia by three or four arches on each side and by both roots; in Osseous Fishes by four; and in the Sharks, Skates, &c. by all the five pairs of branchial vessels and the two roots which are to be found in the early stages of development in the foetus *.

The discovery of the double state of the dorsal and abdominal aorta in the very young fœtus, made by M. Serres, must, however, be regarded as very interesting, not only as it points out a very singular change, little attended to before it was investigated by this author, taking place in the median arteries, but also as it seems to afford an explanation of some varieties in the place of junction of the roots of the aorta, and in the origin of the cœliac, mesenteric and other arteries, which occur in several tribes of reptiles.

The observations of this author in regard to the union of the double arteriæ Basilares and Callosa, will be read with equal interest, as well as several curious facts mentioned by him respecting the union of the principal venous trunks, and the varieties of distribution of the vessels in the umbilical cord in some mammiferous animals.

Dec. 30. 1830.

A. T.

* See Figs. 1. 9. 11. 14. 15. 19. 20. 30. 35. 39. in the two last plates.

In the page above, the formation of the Ductus arteriosus in mammalia has been described in the manner in which Meckel supposed it to take place; but since writing this description, I have made some observations on the foetus of the sow and sheep, which induce me to believe, along with Burdach, that the opinion of Meckel is incorrect, and that the single ductus arteriosus is formed in these and other mammiferous animals in the same manner as one of the two ducts which exist in birds and some reptiles, viz. by the permanence of one of the branchial arches. The fifth branchial arch on the left side, (marked W in fig. 39 of last Plate), is the one which appears to give rise to this communicating vessel in mammalia.

Analysis of a powerful Chalybeate Water from Vicar's Bridge, near Dollar in Clackmannanshire. By ARTHUR CONNELL, Esq. F. R. S. E. Communicated by the Author.

THIS mineral water was first, I believe, observed in the course of last summer, and has excited considerable interest in the neighbourhood of the place where it is found. It has been much used medicinally by the common people of the vicinity; in all probability in many complaints for which it was very ill adapted. It has, however, been found beneficial, when employed with a due regard to its great strength, in some of those diseases for which iron is of advantage; and it has now made its way to other places.

The water is described by my friend Mr Tait, who sent to me a portion of it for analysis, as being found in those mines or excavations from which clay ironstone is obtained at Vicar's Bridge. The excavations are worked out in beds of a kind of shale which contains the iron-ore; and the water forms separate pools on the floor or pavement of the several compartments of the mines. The beds of shale probably form a part of the coal-strata of the neighbourhood, although I have not had any opportunity of examining them. The general appearance of the water of these several pools is described as being much the same, although the solutions are supposed to differ somewhat in strength. That sent to me was conceived to be the strongest impregnation.

The colour of the water was a dark red. Its taste strongly astringent, with some acidity. It reddened litmus paper. Its specific gravity at 62° F. was 1.04893. This high state of concentration constitutes its principal peculiarity. The above specific gravity is considerably greater than that of sea water; and exceeds that of any other natural saline impregnation of which I have read, either in Great Britain or in foreign countries, with the exception of the water of the Dead Sea.

The action of reagents was as follows: With respect to those reactions, showing the presence of iron, I shall be a little particular, with the view of determining the state of oxidation of the iron.

The ferro-prussiate of potash gave immediately a very dark blue precipitate; and when much diluted, the sulpho-cyanate of potash produced a red precipitate. These reactions of course were due to the presence of peroxide of iron.

Recently after the water had come into my possession, it gave with ammonia a dark olive precipitate, becoming reddish by exposure to the air. This reaction showed that some protoxide of iron accompanied the peroxide. After it had been kept some weeks in a corked bottle, it gave a precipitate with ammonia which was reddish-yellow on first falling. With the red cyanuret of iron and potassium, a blue or greenish-blue precipitate fell, either immediately or after a short time. The action with this reagent continued much the same, even after the water had ceased to give a dark-coloured precipitate with ammonia. These appearances also showed the presence of protoxide of iron.

The infusion of nutgalls produced a very fine deep blue, indicating the presence of peroxide of iron, or rather a mixture of the peroxide and protoxide*.

When the precipitate by ammonia was boiled with caustic potash ley, the alkaline solution, examined by ordinary means, showed the presence of alumina.

After precipitating by ammonia, filtering and concentrating considerably by heat, oxalate of ammonia indicated a little lime. When the oxalate of lime had been separated, and the liquid, again concentrated, carbonate of ammonia and phosphate of soda showed the presence of magnesia.

With muriate of baryta, the water, even when considerably diluted, gave a precipitate; showing abundance of sulphuric acid.

When a little of the water was precipitated by ammonia, and the clear liquid considerably concentrated, sulphate of silver caused a slight muddiness, and after a time a very slight precipitate collected, which was dissolved by ammonia; indicating the presence of a minute quantity of muriatic acid.

The constituents of which we have thus found evidence are,

* So great is the concentration of the water, that the resulting mixture is of sufficient consistency to constitute a writing ink; and it has been used by several persons for this purpose, at least when a little gum-arabic has been added to the mixture.