sent off, so that few reach the apex of the column: but the moulding of the ventricle about these is not the cause of the conical figure of the heart, since this obtains where no such mammillary columns are present. (Vol. i. figs. 334-340.) The heart is lined by a membrane, endocardium,' rather thicker and more opaque in the left than in the right cavities, especially in the auricle: thinnest on the muscular projections, both pectinate and columnate. The chief layer consists of a close network of elastic fibres, lined by a stratum of polygonal epithelial scales, constituting the free surface; and attached by an areolar tissue to the muscular coat. This is covered by the reflected serous layer of the heart-bag, called 'ectocardium.' The disposition of the intervening muscular fibres has been best illustrated in relation to the human heart. Those of the auricles appear at the parts not covered by the superficial ones. Some, H, arising from the annulus aorticus,' K, K, arch over the auricle, beneath D, contributing some fibres to the septum, at s: other arched or looped' fibres, F, curve over the auricles and are attached by both extremities to the auriculo-ventricular rings AV and AA: a third series, C, surround the auricular appendages, AA, and encircle the terminations of the superior, cs, and inferior, CI, vena cava. The winding or convolute disposition of these so-called 'annular fibres' is exemplified in fig. 409. The superficial and deep-seated fibres are, however, continuous, at parts of their course those marked E, fig. 408, of the former series, wind round the left auricle LA, and are continuous, with some intervening attachment to the aortic root K, with the ascending band F: a posterior band is shown at G, fig. 409, passing over the left auricle LA, and along the posterior border of the appendix A: some of the fibres, on reaching the anterior border, quit the band G, to join the fibres d forming the apex: other detachments from the band g, encompass the terminations of the pulmonary 409 veins, P, p. Like the muscular fibres of the tongue, those of the heart are not visibly connected together by areolar tissue; such connective medium, in the degree in which it may exist, can only be inferred through the help to unravelling gained by boiling the heart. The more obvious mode of connection is, as in the tongue, by reciprocal decussation or interlocking. LA In the ventricles the longer external fibres, e. g., wind upward round the apex and bend downward from the auricular and arterial rings at the ΓΑ base, to become internal, and so inclose, and, at the same time. contribute to form, the shorter, interposed loops; these, likewise, having similar relations to the layers of fibres which they successively inclose. Evidence of a stratified disposition is, however, progressively narrowed, or shown by smaller tracts of conformable course of fibres, as these are removed in dissection from without inward. In the superficial ventricular layer they have a subspiral course, descending, in the fore part of the ventricles, fig. 410, to the left, and on the back 410 Superficial ventricular fibres; front view. CLXXXVII". part to the right, being partially interrupted at the interventricular grooves, of which the anterior is shown at d. Those which cross the groove bridge over the coronary vessels; those which penetrate it curve upward and contribute to the right layer of the septum, and so help to encompass the right ventricle. The super ficial layer gains in thickness as it approaches the apex, a, where the course of the fibres to the inner surface of the ventricles is well expressed by the term whorl' or vortex,' fig. 411. Those from the fore-part of the heart, d, e, f, enter the apex 411 CLXXXVII". posteriorly those from the back part of the heart, b, enter it anThe curved margin teriorly, at a. of the entering anterior fibres, c, is left entire in successive sections of the apex of the left ventricle, until that of the right ventricle is reached, when a more complex arrangement appears. Most of the entering fasciculi form the innermost layer of almost longitudinal fibres of the ventricular cavities; others are continued into the trabecular and mammillary pro cesses. By reflecting the superficial layer to its attachments or points of inflection at the apex, a, and at the base, b, fig. 412, the second layer is exposed; which is partly formed by fibres 412 ascending from the interior of the right ventricle, CACC, emerging at the posterior coronary tract, pet, and receiving accessions from the aortic and auricular rings. The fibres of this layer, d, take an opposite course from those of the first, b, c. A third layer repeats the general disposition of the superficial one; but a larger proportion of the fibres serve a single ventricle, especially at the apex, CRC. Many fibres of this layer are derived from, or are continued into, the middle layer of the septum, from which, as at fig. 413, b, the layer has been cut, and reflected, at a 2, CRC, exposing the distribution of the internal layers, about each ventricle exclusively, as at rv and I, fig. 413. The interruption of such deep layers is frequent, both by change of direction, as at 4; and by the decussation of fibres to form the great mammillary columns, as shown in the section of such at CC, fig. 413. The right layer of septal fibres, though continuous mainly with the parietal fibres of the right ventricle, curve with their concavity toward the left ventricle, and aid in its compression.' A conception of the plan of arrangement of the muscular fibres of the ventricles may be helped by the diagram, fig. 414. 413 Inner layers of heart-fibres. CXLXXXVIII". The course of the superficial fibres, round both ventricles, is indicated by the band, CPCAAA, from the arterial rings over the 414 fore part of the ventricles, and by the band CACC, over the back part: both combine to form the whorl CRC and R, and gain the interior of the ventricles forming the septum, s, and the carneæ columnæ, cc: the deeper layers surrounding the left. ventricle, LV, are indicated. at RR, CPCAAAAC, and СРСА. Traced from within outward, the fibres from the funicular fasciculus or 'rope,' R, combine with others continued from the two great carneæ columnæ, cc, of the left ventricle, LV, to form the inner series, CRC, which, twining round the apex, close the ventricular cavity, and become superficial: then sweeping spirally from left to right divide into two bands: the longer one first encircles the left ven The fibres of the heart have attachments to fixed points in parts of their course, rather than at definite beginnings or endings: and variations of description may be tricle, as CPCA; then describes a second circle round both ventricles, CPCAA. The band CACC passing down from the aorta, AA, winds over the lower half of the right ventricle, RV, combines with the apical spirals, whence it can be traced obliquely round the left ventricle to terminate at the aortic circle near the anterior coronary tract. The septum ventriculorum consists of three strata, the left and middle belonging to the left ventricle, the right layer exclusively to the right. 6 The contraction of the heart-fibres is called systole,' their relaxation diastole.' The parts of the muscular walls of the heart have different degrees of motion: the inner wall or septum' loses length and breadth, but gains in thickness, during the systole: the outer wall changes these dimensions in a greater degree, with changing relative position to the heart's centre: hence it has been termed the movable' wall, and the septum the fixed' one. The mammillary processes become shorter and thicker cones, and in the degree in which the blood in the ventricles is compressed during systole,' the valves are held by the tendinous cords attached to their free borders and expanding upon their ventricular surface more firmly against eversion, with reflux of blood, into the auricles. The position of the semilunar valves, on the contrary, invites the flow of the blood into the arteries, and forbids return. The trabecula' passing from the 'fixed' to the movable' walls have an analogous function as adding to the resistance of the latter against internal pressure, whence they have been termed 'moderator bands.'1 § 348. Arteries of Mammalia.-The walls of the arterial tube are so strong as to maintain that form when cut across; and so elastic as, then, to retract some way within the areolar or connective tissue, which surrounds the vessel like a sheath. On the inner surface of the tube amyline formifies as elliptical or irregularly polygonal scales, more or less of which show a further stage of condensation, expressed by the term 'nucleate epithelial cell,' fig. 424. The tissue so lined consists of a thin continuous 2 proffered indefinitely as the observers arbitrarily select such attachments under the names of origins' and insertions.' The general conformity of muscular arrangement in the heart of the sheep is shown in CLXXXIX", with that previously demonstrated in the human heart, by the author of CLXXXVII" and CLXXXVIII"; especially in regard to the continuity of certain external with internal fibres. 'CLXXXV". p. 123. 2 I use this term as the correlative of crystallises,' signifying thereby the tendency in dissolved proteine, amyline, or other albuminoid atoms to assume defined size and shape, under given conditions, both in and out of the living body; Rainey has shown how such tendency or property effects the superinduction of organic form upon crystal in the formation of shell (ccix"); and its effects are demonstrated more at large in ccx", |