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arrangement of fibres, mentioned in the text. The manner in which the crystals lie in the tubes is exhibited.

PLATE VI-Fig. 1. Skeleton of the head and shoulder. a, supraoccipital bone; b, paroccipital; c, frontal; d, nasal; e, prefrontal; f, bone of the interorbital septum; g, orbitosphenoid; i, alisphenoid; k, postfrontal; l, mastoid; m, scapula; n, coracoid; o, ulna; p, the bone described in the text as belonging to the row of carpal bones, yet corresponding to the radius in its relations to the coracoid and ulna; q, the bone called clavicle; r, intermaxillary; 8, maxillary; t, palatal; v, dental, articular, and angular portions of the lower jaw; w, entopterygoid; z, hypotympanic; y, mesotympanic; z, epitympanic; 1, operculum; 2, preoperculum, beyond whose posterior and anterior margins are seen projecting the interoperculum and suboperculum.

Fig. 2. View of the muscles. a, muscles of dorsal fin; b, muscles of anal fin; c, c, are placed opposite the most superior and most inferior muscles of the caudal fin; /, small abdominal muscle, arising from the tip of the clavicle, and resting on the peritoneum; e, the other small abdominal muscle, arising from the ulna, and likewise resting on the peritoneum. The peritoneum is torn open inferiorly, so as to exhibit the inferior margin of the liver, and the intestines surrounded by their common investment, together with, f, the peritoneal ligament connecting the liver and intestines; g, the vent.

Fig. 3. A few of the individual muscles of the left side of the anal fin, showing how each muscle is sheathed by that in front, and how the tendons pass into the grooves, and are there invested with sheaths.

XVIII. ON THE STRUCTURE AND COMPOSITION OF THE INTEGUMENT OF THE ORTHRAGORISCUS MOLA. By William Turner, M.B. (Lond.), F.R.S.E., Senior Demonstrator of Anatomy, University of Edinburgh.

SEVERAL noteworthy peculiarities, both structural and chemical, are presented by the integument of the short sun-fish. These I had an opportunity of examining, not only in the specimen dissected by Dr. Cleland, but in one dissected a few years ago by Professor Goodsir and myself. The skin of the latter varied in its thickness in different parts of the body of the animal, from not more than a quarter of an inch to four or five inches. In one examined many years ago by Mr. Goodsir, which was a remarkably large fish, it reached in places as much as six inches.* The great thickness of the skin was produced by an opaque, white, tough and resisting structure, which extended from the tubercle-covered surface of the integument to the loose areolar tissue lying between it and the muscles. When blocks of this white structure were cut off, and set on one side for a short time, a considerable quantity of a pale straw-coloured, serouslooking fluid drained off from them, so as greatly to diminish their

In the Edinburgh Philosophical Journal, vol. 30, p. 188, Mr. Goodsir gives an account of the microscopic characters of the skin of this specimen, which he dissected in 1840, but as he only employed a doublet in the examination, the description is necessarily an imperfect one.

N. H. R.-1862.

size. This fluid heated, either alone, or with nitric acid, gave a flocculent albuminous precipitate. It contained no oil, and exhibited when allowed to cool, after being heated, no tendency to gelatinization. When portions of the white structure were heated in their own fluid, in a water bath, and then allowed to cool, gelatinization took place, which was due, not to any peculiarity of the fluid, but to the chemical composition of the opaque white substance, in the interspaces of which the fluid was infiltrated. Other portions of the skin placed under an exhausted receiver, along with sulphuric acid, shrivelled up to flake-like shavings of glue. The white mass was thus shown to belong to the gelatine-yielding structures, and to have no similarity in composition to the blubber-yielding integument of the cetacea.

course.

From the chemical examination it was probable that this structure was to be regarded as cutis, a supposition which was confirmed by a microscopic examination. When small portions of the cutis were examined in the fresh state, under a magnifying power of 200 diameters, they were found to be composed of a closely arranged network of fine fibres, the exact characters of which could not be clearly studied until they were separated by dissection with needles. (Pl. VI. fig. 4.) It was then seen that the fibres presented certain special peculiarities, which distinguished them from the fibres of ordinary connective tissue. Instead of being collected in fibrillated bundles, each fibre possessed a distinct form and outline, (some being almost twice as broad as others), and extended for some distance, pursuing either a slightly wavy, or a curling tortuous From the very curly nature of many of these fibres I thought that they represented the elastic element of the cutis, but, on the addition of acetic acid, they disappeared in the same manner as the undulating fibres. This observation was repeated on fibres taken from various parts of the cutis, so that it may fairly be stated that the elastic element was either altogether absent from the skin of this fish, or was at a minimum. Throughout the entire thickness of the cutis, the fibres presented a well-marked reticulated arrangement, which distinguished them from that which is generally described to exist in the skin of fishes, where the fibres are mostly disposed in bundles parallel to the free surface, being crossed only at comparatively wide intervals by bundles possessing a vertical direction. In the meshes of this reticulation the abundant fluid of the skin was lodged. Numbers of small, ovoid, elongated, sometimes roundish cells, some of which possessed a single, others two or more nuclei, were also contained in these meshes. (Fig. 4.) These cells were visible, not only in the fresh skin, but after the addition of acetic acid, and even in those slices of the skin which had been digested in the water bath. From the close relation which these cells had to the fibres amongst which they were imbedded, I thought it likely, that, by a careful examination, it might be possible to see processes springing from them in such a manner as to produce that stellated, or

radiated, aspect, which has recently been described by many observers, in connection with the corpuscles of the connective tissue generally. For this purpose I subjected, to repeated observation, portions, not only of the fresh skin, but also sections which had been hardened in spirit, or chromic acid, without being able to convince myself that such stellate connective-tissue corpuscles existed in this cutis.* Passing through the cutis from its deep to the tubercle-covered surface many nerve fibres were seen. In slices of the skin, which had been previously steeped in chromic acid, and then slightly acted on by caustic potash, the nerve fibres appeared, as they approached the deep surface of the tubercles, to present indications of a net-worklike arrangement beneath the tubercles, but not entering in them.

When the free surface of the integument was examined it was seen to consist of a multitude of tubercular plates, large enough to be distinguished by the naked eye, but requiring for their due examination the use of a compound microscope. These tubercles were polygonal in shape, irregularly serrated at their margins, by which serratures they were connected together. (Fig. 5.) A short firm spine projected from the centre of each tubercular plate. In some cases the spine was acuminated at its free extremity, but more generally it was an irregular ridge-like projection, widening out at the base and strengthened laterally by buttresses. These spines gave to the surface of the skin a shagreen-like aspect. A granular pigment was scattered over the surface of many of the plates. In some cases it was collected into stellate, at others into rounded masses, and at others it existed as free scattered granules. It gave to the tubercles a brownish colour, or metallic lustre. It was never found on the apices of the spines, although it frequently extended for some distance up their sides. The tubercles which did not possess any pigment, had a dull white appearance.

Vertical sections through the tubercles and their spines, enabled one to obtain a clearer conception, not only of their structure, but of their relation to the subjacent cutis. (Fig. 6.) The tubercles rested by their deep aspect on the fibrous cutis, with which they were very closely united. The outline of this portion of the cutis was unbroken and continuous, not at all times straight but slightly undulating, and occasionally presenting short digitiform elevations, which might, although did not necessarily, correspond to the position of the spines of the tubercles. The tubercles themselves consisted of two parts, which possessed distinctive microscopic characters, a superficial cuticular and a deeper hard portion, both of which differed structurally and chemically from the subjacent fibrous cutis.

* It is important, therefore, in discussing the presence of corpuscles in connective tissue, to keep in mind, that they may exist in very large numbers in this texture, as in the skin now under consideration, without possessing a radiated and anastomosing arrangement.

The cuticle covered the superficial surface of the tubercles and extended for some distance up the sides of the spines, although I never saw it passing over their free ends. It was continued from the outer surface of one tubercle to that of the adjacent ones, over the serrated apposed margins. In it, and in it only, the pigment of the skin was contained.

The deeper hard part of the tubercle, which owed its great density to the deposition of a calcareous, or other inorganic, material in its substance, formed the chief portion of the tubercle, and the spine projecting from it. It presented very slight traces of structure, a few faint lines, running for the most part horizontally, constituting the only markings on it. The spine had a closely similar aspect, and in many cases appeared to possess a cavity in its interior. In the spine faint lines might be seen, extending in a direction parallel to its long axis. When the tubercles were acted on by hot caustic potash, they were entirely broken up and resolved into a number of particles, some of which were elongated, others irregularly shaped, respecting the nature of which it would be difficult to give a positive opinion. When a portion of the skin was digested in warm caustic potash the tubercles separated from the cutis, whilst the cuticle still remained connected to their outer surfaces. The inference might be drawn from this, that the hard part of the tubercles, like the cuticle, was an epidermal, rather than a dermal structure. Such an inference might possibly, however, be erroneous, as the separation along this line might perhaps be due to the alkali acting more readily on the fibrous cutis than on the different parts of the tubercle. An absolute opinion as to the homology of the tubercles could only be given by tracing the manner of their development.

By digestion in hydrochloric acid the inorganic material was dissolved out of the hard part of the tubercle.

ILLUSTRATIONS.

PLATE VI. Fig. 4.-Fibres and cells of cutis. × 200 diam. This figure simply gives the anatomical elements of the cutis, as seen in a portion which has been dissected with needles. The cellular element bears a larger proportion to the fibrous element than has here been represented.

Fig. 5. Surface view of integument, showing serrations at margins of tubercular plates, central spines, and various forms of pigment arrangement. x 45 diam. Fig. 6.-Section through tubercular plate with its spine, and subjacent cutis. X 120 diam.

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