been observed with regard to the termination of these fibres, for future and more successful researches will probably modify the views now held with regard to this point. Kölliker' states that the fibres in question are very fine, dark-bordered tubes, with a medullated sheath, which, when studied in

Mode of termination of the motor nerves, after Rouget.

A. Primitive fasciculus of the thyro-hyoid muscle of the human subject, and its nerve-tube.1, 1, primitive muscular fasciculus; 2, nerve-tube; 3, medullary substance of the tube, which is seen extending to the terminal plate, where it disappears; 4, terminal plate situated beneath the sarcolemma, that is to say, between it and the elementary fibrilla; 5, 5, sarcolemma. B. Primitive fasciculus of the intercostal muscle of the lizard, in which a nerve-tube terminates.-1, 1, sheath of the nerve-tube; 2, nucleus of the sheath; 3, 3, sarcolemma becoming continuous with the sheath; 4, medullary substance of the nerve-tube ceasing abruptly at the site of the terminal plate; 5, 5, terminal plate; 6, 6, nuclei of the plate; 7, 7, granular substance which forms the principal element of the terminal plate, and which is continuous with the axis-cylinder; 8, 8, undulations of the sarcolemma reproducing those of the fibril; 9, 9, nuclei of the sarcolemma. (LONGET, Traité de Physiologie, Paris, 1869, tome iii., p. 99.)

muscular tissue rendered pale by acetic acid, may be seen to give off exceedingly fine, non-medullated fibres, which terminate in fibres of the same appearance, but provided with nuclei. It does not appear to be certain how these fibres end. Kölliker is not satisfied that the free extremities, as they appear to be, are the actual terminations; but he asserts that in some rare instances they communicate with each other. For the present this point must be considered as unsettled.

Mode of Termination of the Nerves in the Involuntary Muscular Tissue.-The nerves have not been followed out

1 KÖLLIKER, op. cit., p. 228.

so satisfactorily in the involuntary as in the striated muscular system; and as most, if not all of the fibres are derived from the sympathetic system, which contains numerous fibres of Remak the terminations of which have not been described, it is evident that our information concerning this part of the peripheral nervous system must be incomplete. Perhaps the most remarkable of the late observations upon this point are those of Dr. Frankenhaeuser, upon the nerves of the uterus. These researches were very elaborate; but the point most interesting in this connection is that the nerves, having formed a plexus in the connective tissue, send exceedingly small fibres into the sheets or layers of muscular-fibre cells, which branch and finally go into the nucleoli of these structures.' Arnold has confirmed these observations, and has shown farther that in many instances the fine terminal nerve-fibres branch and go into the nuclei of the muscular fibres, and then pass out to join with other fibres and form a plexus.'

Termination of the Nerves in Glands.-The great influence which the nervous system exerts upon secretion attaches considerable interest to recent researches into the ultimate distribution of the nerves in the glands. It must be remembered, however, in these, as in all observations upon the destination of the smallest nerve-fibres, that the problem is one of the most difficult in the whole range of minute anatomy; and the results arrived at must be received

1 FRANKENHAEUSER, Die Nerven der Gebaermutter und ihre Endigung in den glatten Muskel-fasern, Jena, 1867, S. 76, Taf. viii.

2 ARNOLD, in STRICKER, Manual of Human and Comparative Histology, London, 1870, vol. i., p. 195, et seq. The exact mode of termination of the nerves in the organic muscles cannot be regarded as definitively settled. We have attempted, however, to give what seem to be the most reliable views on this sub. ject, deduced from recent observations. For a further discussion of some of the points which we have accepted as probable, the reader is referred to a recent article by Krause. (Die Nervenendigung in den glatten Muskelen.—Archiv für Anatomie, Physiologie und wissenschaftliche Medicin, Leipzig, 1870, S. 1, et seq.)

with a certain amount of caution, until they shall have been amply confirmed.

The researches of Pflüger upon the salivary glands leave no doubt as to the fact that medullated nerve-fibres pass to the cells of these organs and there abruptly terminate, at least as dark-bordered fibres. This author believes, however, that, having formed a more or less branching plexus, non-medullated fibres pass directly into the glandular cells, and he gives figures which seem to illustrate this arrangement pretty clearly. The same observer describes and figures multipolar cells, mixed with the glandular cells, in which some of the nerve-fibres terminate.'

Modes of Termination of the Sensory Nerves.-There are undoubtedly several modes of termination of the sensitive nerves in integument and mucous membranes, some of which have been accurately enough described, while others are still somewhat uncertain. In the first place, anatomists now recognize three varieties of corpuscular terminations, differing in their structure, probably, according to the different functions connected with sensation, with which the parts are endowed. In addition, it is probable that many sensitive nerves are connected with the hair-follicles, which are so largely distributed throughout the cutaneous surface. There are, also, terminal filaments not connected with any special organs, some of them, perhaps, ending simply in free extremities, and some connected with epithelium. There is still considerable difference of opinion among anatomists

1 PFLÜGER, in STRICKER, Manual of Human and Comparative Histology, London, 1870, vol. i., p. 433, et seq. The views here advanced by Pflüger have been confirmed by him in more recent observations and extended to the pancreas (Journal of Anatomy and Physiology, Cambridge and London, 1870, vol. iv., p. 156). Pflüger states, also, his belief that the same connection exists between the nerves and the liver-cells (ibid., p. 188). The question, however, is still somewhat uncertain, and Mayer, in examinations of the salivary glands, found filaments in connection with the nuclei, but failed to satisfy himself that they were nervous (Quarterly Journal of Microscopical Science, London, April, 1870, p. 199)

concerning all of these various points, but with regard to the terminal corpuscles, these differences are purely anatomical, and do not materially affect the physiology of sensation. We do not propose, therefore, to enter fully into the discussions upon these questions, and will simply present what seem to be the most reasonable views of the latest and most reliable observers.

Corpuscles of Pacini, or of Vater.-These corpuscles, which were the first discovered and described in connection with the sensitive nerves, were called corpuscles of Pacini, until it was shown that they had been seen about a century and a half ago by Vater. Their actual mode of connection with the nerves, however, has only been ascertained within the last few years. The following are the measurements of these bodies and the situations in which they are found, taken from Kölliker: '

In man, these corpuscles are oval or egg-shaped, and measure from to of an inch in length. They are always found in the subcutaneous layer on the palms of the hands and the soles of the feet, and are most numerous on the palmar surfaces of the fingers and toes, particularly the third phalanges. In the entire hand there are about six hundred, and about the same on the feet. They are sometimes, but not constantly, found in the following situations: The dorsal surfaces of the hands and feet; on the cutaneous nerves of the arm, the forearm and the neck, the internal pudic nerve, the intercostal nerves, all of the articular nerves of the extremities, the nerves beneath the mammary glands, the nerves of the nipples, and in the substance of the muscles of the hands and feet. They are found without exception on all of the great plexuses of the sympathetic system, in front of and by the sides of the abdominal aorta, and behind the peritoneum, particularly in the vicinity of the

1 KÖLLIKER, Éléments d'histologie humaine, Paris, 1868, p. 141.

pancreas. They sometimes exist in the mesentery, and have been observed near the coccygeal gland.

-d

..C

The structure of the corpuscles consists simply of several layers of connective tissue enclosing a central bulb in which is found the terminal extremity of the nerve. This bulb is finely granular, nucleated, and is considered by most anatomists to be composed of connective tissue. At the base of the corpuscle is a pedicle formed of connective tissue surrounding a medullated nervefibre which penetrates the corpuscle and terminates in the central bulb.

The only really important point of discussion with reference to the structure of the nerve-fibre in the central bulb, and this is purely anatomical, is whether or not the medullary substance extends into the corpuscle itself. Probably the fibre is here reduced simply to the axis-cylinder. Kölliker Pacinian corpuscle from the human subject, thinks that there is a very thin

magnified 350 diameters.-a, pedicle of the

corpuscle; b, nerve-fibre contained in its

interior; c, external layer of its covering; layer of medullary substance, d, internal layer; e, pale nerve-fibre within but he states that this is a questhe internal transparent bulb; f. divisions and extremities of the fibre. (KÖLLIKER, tion difficult to decide.' All Handbuch der Gewebelehre, Leipzig, 1867,

S. 108.)

anatomists agree that a single thin, flat fibre penetrates the corpuscle and terminates near its summit in two or three branches, with slightly enlarged

1 Op. cit., p. 143.