In certain situations, e.g., immediately beneath the lining membrane of the ventricles, the cardiac muscular tissue shows a peculiar modification in the form of a network of clear beaded fibres, just visible to the naked eye, which were described by Purkinje, and are known by his name. When examined with the microscope they are seen to be composed of large clear quadrangular cells; each usually contain two nuclei near the centre, with a little granular protoplasm around the nuclei. At the margin of the cells are columns of transversely striated muscle-substance, which partly surround the cells and appear to join with the muscle-columns of adjacent cells, so as to produce the aspect of an open network of muscular fibres with large cells occupying its meshes. The most probable explanation of this appearance is that these are cells of the muscular tissue the differentiation of which has been arrested at an early stage of their development, and that the cells themselves have continued to grow without any further formation of the cross-striated substance. Like the skeletal muscles the heart-muscle is richly supplied with blood-vessels. The muscular tissue differs, however, from that of ordinary skeletal muscles in the large supply of lymphatic vessels with which it is provided. The lymphatics, in fact, occupy almost all the interstices of the muscular network, so that the muscular substance is like a sponge, the meshes of which are occupied by lymph. The nerves which are supplied to the cardiac fibres are all non-medullated near their terminations. Their manner of ending will be afterwards considered. RECENT LITERATURE OF THE MUSCLES. Babinski, J., Des modifications que présentent les muscles à la suite de la section des nerfs qui s'y rendent, Comptes rendus, t. 98, 1884. Ballowitz, E., Fibrilläre Structur und Contractilität, Pflüger's Archiv, Bd. xlvi., 1889. Barfurth, D., Die Rückbildung des Froschlarvenschwanzes und die sogenannten Sarkoplasten, Archiv f. mikrosk. Anatomie, Bd. xxix., 1887. Bremer, L., Ueber die Muskelspindeln nebst Bemerkungen über Structur, Neubildung und Innercation der quergestreiften Muskelfaser, Arch. f. mikr. Anat., Bd. xxii., 1883. Busachi, T., Ueber die Regeneration der glatten Muskeln, Medic. Centrabl., 1887. Bütschli u. Schewiakoff, Ueber den feineren Bau der quergestreiften Muskeln bei Arthropoden, Biol. Centralbl., Feb., 1891. Ciaccio, G. V., Sur l'anatomie microscopique des muscles qui servent à mouvoir les ailes des insectes, Archives ital. de biologie, t. ii., 1882; Dell' anatomia minuta di quei muscoli che negl'insetti muovono le ali, Memorie della reale accad. delle scienze di Bologna, Serie IV., t. viii., 1887. Emery, Sur la structure des fibres musculaires striées de quelques vertébrés, Archives ital. de biol., ii., 1882. Exner, S., Veber optische Eigenschaften lebender Muskelfasern, Pflüger's Archiv, Bd. Ix., 1887. Fantino, G., Sur les altérations du myocarde après la section des nerfs extracardiaques, Archives italiennes de biologie, x., 1888. Felix, W., Die Länge der Muskelfaser bei dem Menschen und einigen Säugethieren, Festschrift f. A. v. Kölliker, 1887; Theilungserscheinungen an quergestreiften Muskeln menschlicher Embryonen, Anatom. Anzeiger, 1888; Ueber Wachsthum der quergestreiften Musculatur nach Beobachtungen am Menschen, Zeitschr. f. wiss. Zool., Bd. xlviii., 1889. Franqué, O. v., Beitr. z. Kenntniss der Muskelknospen, Wurzburg Verhandl., 1890. Gage, S. P., Form, endings, and relations of striated muscular fibres in the muscles of minute animals (mouse, shrew, bat and English sparrow), The Microscope, Detroit, 1888. Gehuchten, A. van, Etude sur la structure intime de la cellule musculaire striée, La Cellule, t. ii., 1886, and t. iv., 1888; Les noyaux musculaires de la grenouille adulte, Anat. Anz. iv., 1888; Cellules musculaires striées ramifiées et anastomosées, Anat. Anz., Suppl. Heft, 1889. Goldenburg, B., Untersuchungen über die Grossenverhältnisse der Muskelfasern des normalen, sowie des atrophischen und des hypertrophischen Herzens des Menschen, Dissert., Dorpat, 1885. Grützner, P., Zur Anatomie und Physiologie der quergestreiften Muskeln, Recueil Zoologique Suisse, 1884. Haswell, W. A., A comparative study of striated muscle, Quart. Journ. of Microsc. Science, xxx.,1889. Haycraft, J. B., On the minute structure of striped muscle, with special allusion to a new method of investigation, by means of "impressions" stamped in collodion, Proc. Roy. Soc., vol. 49, 1891.2 1 The student is referred to these articles for the older Bibliography of the subject. 2 Haycraft has endeavoured to show that the cross-markings upon a muscle-fibre are nothing but the optical effect of varicosities of the component fibrils, since impressions of muscle in collodion reproduce most of the cross-striated appearances. But this fact is entirely insufficient to prove the point, for it is clear that a difference in consistence of the different parts of the muscle-element would alone lead to the reproduction by the impression-method, and in view of the entirely different optical and chemical properties of the different parts of the muscle-element, such a position is quite untenable. Kerschner, L., Bemerkungen über ein besonderes Muskelsystem im willkürlichen Muskel, Anatom. Anzeiger, 1888. Knoll, Ph., Ueber helle und trübe, weisse u. rote quergestreifte Muskulatur, Wiener Akademie Sitzungsb., 1889. Kölliker, A. v., Zur Kenntniss der quergestreiften Muskelfasern, Zeitschrift für wissensch. Zoologie, Bd. lxvii., 1888; Handbuch der Gewebelehre, 1890. Kühne, W., Verhandl. d. naturh. med. Vereins z. Heidelberg, 1884, &c.; and Zeitschr. f. Biol., 1886. Kultschizny, N., Ueber die Art der Verbindung der glatten Muskelfasern miteinander, Biologisches Centralbl. vii., 1887. Kunkel, A. J., Studien über die quergestreifte Muskelfaser, Festschrift für A. v. Kölliker, 1887. Laulanié, F., Sur les phénomènes intimes de la contraction musculaire, dans les faisceaux primitifs striés, Comptes rendus, t. 101, 1885. Limbeck, R. v., Ueber morphologische Verschiedenheiten quergestreiften Muskelfasern, Prager medic. Wochenschr., 1885; Zur Kenntniss des Baues der Insektenmuskeln, Sitzungsber. der Wiener Akad., Bd. 91, 1885. Macallum, A. B., On the nuclei of the striated muscle-fibre in Necturus (Meno-branchus) lateralis, Quart. Journal of Micr. Science, March, 1887. Marshall, C. T., Observations on the structure and distribution of striped and unstriped muscle in the animal kingdom and a theory of muscular contraction, Quart. Journ. of Microsc. Science, 1887; Further observations, &c., Ibid., 1889. Mayeda, R., Ueber die Kaliberverhältnisse der quergestr. Muskelfasern, Zeitschr. f. Biol., 1890. Mayer, S., Zur Histologie des quergestreiften Muskels, Biolog. Centralbl. iv., 1884; Die sogenannten Sarkoplasten, Anat. Anzeiger, 1886; Einige Bemerkungen zur Lehre von der Rückbildung quergestreifter Muskelfasern, Prager Zeitschr. f. Heilkunde, Bd. viii., 1887. Melland, B., A simplified view of the histology of the striped muscle-fibres, Quart. Journ. of Micr. Science, July, 1885. Mingazzini, P., Sul preteso reticolo plastinico della fibra muscolare striata, Bollettino della Società di Naturalisti in Napoli, 1888; Contributo alla cognoscenza della fibra muscolare striata, Anat. Anz., 1889. Müller, G. E., Die Theorie der Muskel-contraction, Nachrichten von der kgl. Gesellsch. der Wissensch. zu Göttingen, 1889. Nauwerck, C., Ueber Muskelregeneration u. Verletzungen, Jena, 1890. Navalichin, Genèse et mort des fibres musculaires chez l'animal supérieur adulte à l'état normal, Archives slaves de biol., t. i., 1886. Nikolaides, R., Ueber die mikroskopischen Erscheinungen bei der Contraction des quergestreiften Muskels, Arch. f. Anat. u. Physiol., Physiol. Abth., 1885. Paneth, J., Die Entwicklung von quergestreiften Muskelfasern aus Sarkoplasten, Sitzungsberichte d. Wiener Akademie, Bd. 92, 1885; Zur Frage nach der Natur der Sarkoplasten, Anatom. Anzeiger, 1887. Ramon y Cajal, S., Observations sur la texture des fibres musculaires des pattes et des ailes des insectes, Internationale Monatsschrift f. Anatomie, Bd. v., 1888. Ranvier, L., Des muscles rouges et des muscles blancs chez les rongeurs, Compt. rend., t. 104, 1887; Des muscles de la vie animale à contraction brusque et à contraction lente, chez le lièvre, Compt. rend., t. cvii., 1889. Retzius, G., Muskelfibrille u. Sarcoplasma, Biologische Untersuchungen, Neue Folge, Stockholm, 1890. Robert, F., Ueber Wiederbildung quergestr. Muskelf., Diss., Kiel, 1890. Rollett, A., Untersuchungen über den Bau der quergestreiften Muskelfasern, Denkschriften der Wiener Akad., Bd. 49 und 51, 1885; Ueber die Flossenmuskeln des Seepferdchens (Hippocampus antiquorum) und über Muskelstruktur im Allgemeinen, Archiv f. mikrosk. Anat., Bd. xxxii., 1888; Anat. u. physiol. Untersuchungen ü. d. Muskeln der Fledermäuse, Wiener Sitzungsb., 98, 1889. Schäfer, E. A., On the minute structure of the wing-muscles or sarcostyles which form the wingmuscles of insects. Preliminary note, Proc. Roy. Soc., vol. 49, 1891, with two photographic plates; On the structure of amaboid protoplasm, with a comparison between the nature of the contractile process in amaboid cells and in muscular tissue, &c., Ibid., 1891; On the structure of cross-striated muscle, Monthly International Journal of Anatomy and Physiology, vol. viii., 1891. Schwalbe, Ueber die Kaliberverhältnisse der quergestr. Muskelf. der Wirbelthiere, Deutsche med. Wochenschr., 1890, No. 35. Schwalbe u. Mayeda, Ueber die Kaliberverhältnisse d. quergestr. Muskelf. des Menschen, Zeitschr. f. Biol., 1891. Wagener, G. R., Die Entstehung der Querstreifen auf den Muskeln, Pflüger's Arch., Bd. 30, 1883. Walther, F., Ueber Wachsthum der quergestreiften Musculatur nach Beobachtungen am Menschen, Zeitschr. f. wiss. Zool., Bd. xlviii., 1889. NERVOUS SYSTEM. The nervous system consists of a central part, or rather a series of connected central organs, named the cerebro-spinal axis, or cerebro-spinal centre; and of the nerves, which have the form of cords connected by one extremity with the cerebrospinal centre, and extending from thence through the body to the muscles, sensible parts, and other organs placed in functional relation with them. The nerves form the medium of communication between these distant parts and the centre. One class of nervous fibres, termed afferent or centripetal, conducts impressions towards the centre, another, the efferent or centrifugal, carries stimuli from the centre to the periphery. Besides the cerebro-spinal centre and the nervous cords, the nervous system comprehends also certain bodies named ganglia, which are connected with the nerves in various situations. These bodies, though of much smaller size and less complex nature than the cerebro-spinal centre, agree, in some respects, with that organ in their elementary structure, and to a certain extent also in their relation to the nervous fibres with which they are connected; and this correspondence becomes even more apparent in the nervous system of the lower members of the animal series. The nerves are divided into the cerebro-spinal, and the sympathetic nerves. The former are distributed principally to the skin, the organs of the senses, and other parts endowed with manifest sensibility, and the muscles. They are, for the most part, attached in pairs to the cerebro-spinal axis, and like the parts which they supply are, with few exceptions, remarkably symmetrical on the two sides of the body. The sympathetic nerves, on the other hand, are destined chiefly for the viscera and blood-vessels, of which the movements are involuntary, and the natural sensibility is obtuse. They differ also from the cerebro-spinal nerves in having generally a greyish or reddish colour, in their less symmetrical arrangement, and especially in the circumstance that the ganglia connected with them are much more numerous and more widely distributed. Branches of communication pass from many of the spinal nerves at a short distance from their roots, to join, and in fact to form, the sympathetic, which is thus seen to be merely an offset from the cerebrospinal centre, as indeed its mode of development (see EMBRYOLOGY) Would also appear to show. The nervous system is made up of a substance proper and peculiar to it, with inclosing membranes, nutrient blood-vessels and supporting connective tissue. The nervous substance has been long distinguished into two kinds, obviously differing from each other in colour, and therefore named the white, and the grey or cineritious. When subjected to the microscope, the nervous substance is seen to consist of two different structural elements, viz., fibres and cells. The fibres are found universally in the nervous cords, and they also constitute the greater part of the nervous centres: the cells on the other hand are confined in a great measure to the cerebro-spinal centre and the ganglia, and do not exist generally in the nerves properly so called, although they are found at the terminations of some of the nerves of special sense, and also interposed here and there among the fibres of particular nerves; they are contained in the grey portion of the brain and spinal cord, and in the ganglia. NERVE FIBRES. Two kinds of nerve-fibres are met with in the body, differing from one another both in their microscopical character and in their more obvious aspect: those of the one kind have received the name of white fibres, on account of the appearance which they present when collected in considerable numbers, as in the nerve trunks or white matter of the nerve centres, the others being denominated grey fibres. When examined with the microscope it is found that this difference of aspect depends upon the presence or absence of a peculiar sheath to the fibre, formed of a kind of fatty substance, this fatty or medullary substance, as it is termed, giving a dark double contour to the white fibres (when seen by transmitted light), which is Fig. 352.-WHITE OR MEDULLATED NERVE-FIBRES, SHOWING THE SINUOUS OUTLINE AND Fig. 353.-A SMALL PART OF A MEDULLATED FIBRE HIGHLY MAGNIFIED (E. A. S.). The fibre looks in optical section like a tube-hence the term tubular, formerly applied to these fibres. Two partial breaches of continuity are seen in the medullary sheath, which at these places exhibits a tendency to split into laminæ. The primitive sheath is here and there apparent outside the medullary sheath, and the delicate striæ which are visible in the middle of the fibre probably indicate the fibrillated axis-cylinder. Fig. 354.-VARICOSE MEDULLATED FIBRES FROM THE ROOT OF A SPINAL NERVE (from Valentin). altogether absent from those of the other kind. On account of this the white fibres are also known as the double-bordered or medullated fibres, the grey fibres being termed in contradistinction the pale or non-medullated fibres, or from their discoverer, the fibres of Remak. The medullated nerve-fibres form the white part of the brain and spinal cord, and by far the greater part of the cerebro-spinal nerves. Viewed singly under the microscope with transmitted light they are transparent, and, as before stated, are characterised by their well-defined even outline and, except the smallest, by their double contour, which gives them a tubular aspect. Their size differs considerably even in the same nerve, but much more in different parts of the nervous system; some being less than 12th inch (2μ), and others upwards of th inch (17) in diameter. Speaking generally, they 00 may be divided into three sets or kinds according to their size. Thus, most fibres which are found in the ordinary or cerebro-spinal nerves are from 8μ to 16μ in diameter; whereas those which pass from the roots of the spinal nerves to the sympathetic average only from 18μ to 36μ, while fibres of an intermediate size occur in large numbers in the vagus, the glosso-pharyngeal, the facial, and in the motor root of the fifth nerve as well as in the anterior roots of the spinal nerves (Gaskell). These differences are illustrated in fig. 384, p. 329. Many of the medullated nerve-fibres appear dilated or swollen out at short distances along their length, and contracted in the intervals between the dilated parts. These fibres, however, are naturally cylindrical like the rest, and continue so while they remain undisturbed in their place; and the varicose character is occasioned by pressure or traction during the manipulation, which causes the soft matter to accumulate at certain points, whilst it is drawn out and attenuated at others (fig. 354), The fibres in which this is most apt to occur are usually of small size, ranging from toth of an inch in diameter; and when a very small fibre is thus affected, the varicosities appear like a string of globules held together by a fine transparent thread. Structure of medullated fibres.-The medullated fibres are composed for the most part of three distinct structures, viz., an axial fibre (the axis-cylinder of Fig. 355.-DIAGRAM to show the parts of a medullated fibre, viz., 1, 1, outer or primitive sheath enclosing the doubly contoured white substance or medullary sheath. 2, a part where the white substance is interrupted, the outer sheath remaining. 3, axis cylinder projecting beyond the broken end of the tube. 4, part of the contents of the tube escaped. Fig. 356.-Two PORTIONS OF MEDULLATED NERVE FIBRES, AFTER TREATMENT WITH OSMIC ACID, SHOWING THE AXIS-CYLINDER, AND THE MEDULLARY AND PRIMITIVE SHEATHS (Key and Retzius). A. Node of Ranvier. B. Middle of an internode with nucleus. c, axis-cylinder, projecting at the broken end; p, primitive sheath within which the medullary sheath, which is stained dark by the osmic acid, is somewhat retracted. Fig. 357.-PART OF AN AXIS-CYLINDER, HIGHLY MAGNIFIED, SHOWING THE FINE VARICOSE FIBRILS WITHIN IT (Max Schultze). Purkinje), enclosed within two sheaths, one of these being the medullary sheath already mentioned, and the other a delicate membranous tube outside of all, termed the nucleated sheath of Schwann, the primitive sheath, or the neurolemma. But there are medullated fibres in which the primitive sheath is absent, and other fibres and prolongations of fibres in which there is no sheath whatever to the axis-cylinder. 1 The term neurilemma or neurolemma was formerly applied to the connective tissue sheath of the funiculus (see p. 325), which is now known as the perineurium. |