large size, and constantly associated with small hair-follicles. In the meatus auditorius the ceruminous glands are also large; in the eyelids the cilia are supplied like other hairs with sebiparous glands, but the Meibomian glands may also be regarded as belonging to this class. The excretory ducts of sebiparous glands offer some diversity in different parts of the body; in many situations they are short and straight, in others, as in the palms of the hands and soles of the feet, where the epidermis is thick, they assume a spiral course. rous ducts are lined by an inversion of the epidermis, which forms a thick and funnel-shaped cone at its commencement, but soon becomes uniform and soft. Sebiparous glands are met with in all parts of the body, but are most abundant in the skin of the face, and in those situations which are naturally exposed to the influence of friction.

The sebife

The sebaceous substance, when it collects in inordinate quantities within the excretory ducts, becomes the habitat of a remarkable parasitic animal, the steatozoon folliculorum.

The SUDORIPAROUS GLANDS are situated deeply in the corium and also in the subcutaneous areolar tissue, where they are surrounded by adipose cells. They are small round or oblong bodies, composed of one or more convoluted tubuli, or of a congeries of glandular vesicles, which open into a common efferent duct. The latter ascends from the gland through the derma and epidermis, and terminates on the surface by a funnel-shaped and oblique aperture or pore. The efferent duct presents some variety in its course upwards; within the derma it is straight, or curved and serpentine, and if the epidermis be thin, proceeds more or less directly to the excreting pore. Sometimes it is spirally curved within the derma, and having passed the latter, is regularly and beautifully spiral in its passage through the epidermis, the last turn forming an oblique and valvular opening on the surface. The spiral course of the duct is especially remarkable in the thick epidermis of the palm of the hand and sole of the foot. On those parts of the skin where the papillæ are irregularly distributed, the efferent ducts of the sudoriparous glands open on the surface also irregularly, while on the palmar and plantar surfaces of the hands and feet, the pores are situated at regular distances along the ridges, at points corresponding with the intervals of the small, square-shaped, clumps of papillæ. Indeed the apertures. of the pores, seen on the surface of the epidermal ridges, give rise to the appearance of small transverse furrows, which intersect the ridges from point to point.

The efferent duct and the glandular vesicles and tubuli of the sudoriparous gland are lined by an inflection of the epidermis. This inflection is thick and infundibuliform in the upper stratum of the derma, but soon becomes uniform and soft. The infundibuliform projection is drawn out from the duct when the epidermis is removed, and may be perceived on the under surface of the latter as a nipple-shaped cone. A good view of the sudoriferous ducts is obtained by gently separating the epidermis of a portion of decomposing skin; or they may be better seen by scalding a piece of skin, and then withdrawing the epidermis from the derma. In both cases it is the lining sheath of epidermis, in other words, the epithelium which is drawn out from the duct.

CHAPTER XI.

OF THE VISCERA.

THAT part of the science of anatomy which treats of the viscera is named splanchnology, from the Greek words, onλáyzvov, viscus, and aóyos. The viscera of the human body are situated in the three great internal cavities; cranio-spinal, thorax, and abdomen. The viscera of the cranio-spinal cavity, namely, the brain, and spinal cord, with the principal organs of sense, have been already described, in conjunction with the nervous system. The viscera of the chest are: the central organ of circulation, the heart; the organs of respiration, the lungs; and the thymus gland. The abdominal viscera admit of a subdivision into those which properly belong to that cavity, viz., the alimentary canal, liver, pancreas, spleen, kidneys, and supra-renal capsules; and those of the pelvis, the bladder and internal organs of generation.

THORAX.

The thorax is the conical cavity, situated at the upper part of the trunk of the body it is narrow above, and broad below, and is bounded in front, by the sternum, six superior costal cartilages, ribs, and intercostal muscles; laterally, by the ribs and intercostal muscles; and, behind, by the ribs, intercostal muscles, and vertebral column, as low down as the upper border of the last rib and first lumbar vertebra; superiorly, by the first rib at each side, the upper part of the sternum in front and the first dorsal vertebra behind; and, inferiorly, by the diaphragm. The superior opening of the thorax is closed by the thoracic fascia, and gives passage to the following parts, namely, the sterno-hyoid, sternothyroid, and longi colli muscles; the trachea and oesophagus; the carotid and subclavian arteries and veins, and thoracic duct; the pneumogastric, phrenic, and sympathetic nerves; and the upper part of the lungs and pleura. The cavity of the thorax is much deeper on the posterior than on the anterior wall, in consequence of the obliquity of the diaphragm, and contains the heart inclosed in its pericardium, with the great vessels; the lungs, with their serous coverings, the pleurae; the oesophagus; some important nerves; and, in the fœtus, the thymus gland.

THE HEART.

The central organ of circulation, the heart, is situated between the two layers of pleura which constitute the mediastinum, and is inclosed in a proper membrane, the pericardium.

Pericardium. - The pericardium is a fibro-serous membrane like the dura mater, and resembles that membrane also in deriving its serous layer from the reflected serous membrane of the viscus which it incloses. It consists of two layers, external, fibrous; and internal, serous. The fibrous layer is attached. above, to the great vessels procceding from the heart, on which it is continuous with the thoracic fascia; and below, to the tendinous portion of the diaphragm. The serous membrane invests the heart with the commencement of its great vessels as high as the arch of the aorta, and is then reflected upon the internal surface of the fibrous layer.

In intimate structure the fibrous layer is composed of areolar tissue; the serous layer consisting of a thin stratum of elastic tissue disposed in a network,

adherent by one surface to the fibrous layer, and smooth on the free surface, where it gives support to a single or double lamina of tesselated epithelium. The bag of the pericardium has few vessels and nerves, the latter being derived from the phrenic and recurrent branch of the right pneumogastric.

The HEART is placed obliquely in the chest, the base being directed upwards and backwards towards the right shoulder; the apex forwards and to the left, pointing to the space between the fifth and sixth ribs, at about two or three inches from the sternum.' Its under side is flattened, and rests on the tendinous portion of the diaphragm; its upper side is rounded and convex, and formed principally by the right ventricle, and partly by the left. Surmounting the ven

ANATOMY OF THE HEART. 1. Right auricle. 2. Entrance of the superior vena cava. 3. Entrance of the inferior cava. 4. Opening of the coronary vein, half-closed by the coronary valve. 5. Eustachian valve. 6. Fossa ovalis, surrounded by the annulus ovalis. 7. Tuberculum Loweri. 8. Musculi pectinati of the appendix auriculæ. 9. Auriculo-ventricular opening. 10. Cavity of the right ventricle. 11. Tricuspid valve, attached by the chordæ tendineæ to the carneæ columnæ (12). 13. Pulmonary artery, guarded at its commencement by three semilunar valves. 14. Right pulmonary artery, passing beneath the arch and behind the ascending aorta. 15. Left pulmonary artery, crossing in front of the descending aorta. Remains of the ductus arteriosus, acting as a ligament between the pulmonary artery and arch of the aorta. The arrows mark the course of the venous blood through the right side of the heart. Entering the auricle by the superior and inferior cave, it passes through the auriculo-ventricular opening into the ventricle, and thence through the pulmonary artery to the lungs. 16. Left auricle. 17. Openings of the four pulmonary veins. 18. Auriculo-ventricular opening. 19. Left ventricle. 20. Mitral valve, attached by its chordæ tendineæ to two large columnæ carnea, which project from the walls of the ventricle. 21. Commencement and course of the ascending aorta behind the pulmonary artery, marked by an arrow. The entrance of the vessel is guarded by three semilunar valves. 22. Arch of the aorta. The comparative thickness of the two ventricles is shown in the diagram. The course of the pure blood through the left side of the heart is marked by arrows. The blood is brought from the lungs by the four pulmonary veins into the left auricle, and passes through the auriculo-ventricular opening into the left ventricle, whence it is conveyed by the aorta to every part of the body.

tricles are the corresponding auricles, whose auricular appendages are directed forwards, and slightly overlap the root of the pulmonary artery. The pulmonary artery is the large anterior vessel at the root of the heart; it crosses obliquely

The size of the heart is about five inches in length, three and a-half inches in greatest breadth, and two and a-half in thickness. Its weight is about eleven ounces in the male, and nine ounces in the female.

the commencement of the aorta. The heart consists of two auricles and two ventricles, which are respectively named, from their position, right and left. The right is the venous side of the heart; it receives into its auricle the venous blood from every part of the body, by the superior and inferior cava and coronary vein. From the auricle the blood passes into the ventricle, and from the ventricle through the pulmonary artery, to the capillaries of the lungs. From these it is returned as arterial blood to the left auricle; from the left auricle it passes into the left ventricle; and from the left ventricle is carried through the aorta, to be distributed to every part of the body, and again returned to the heart by the veins. This constitutes the course of the adult circulation.

The heart is best studied in situ. If, however, it be removed from the body, it should be placed in the position indicated by the above description of its situation. A transverse incision should then be made along the ventricular margin of the right auricle, from the appendix to its right border, and crossed by a perpendicular incision, carried from the side of the superior to the inferior The blood must then be removed. Some fine specimens of white fibrin are frequently found with the coagula; occasionally they are yellow and gelatinous. The older anatomists called these substances "polypus of the heart:" they are usually met with in the right ventricle, and sometimes in the left cavities.

cava.

The RIGHT AURICLE is larger than the left, and consists of a principal cavity or sinus, and an appendix auricula. The interior of the sinus presents for examination five openings; two valves; two relicts of foetal structure; and two peculiarities in the proper structure of the auricle. To facilitate remembrance they may be thus arranged:

Openings

Valves

:

Relicts of fatal structure

Structure of the auricle.

Superior cava,

Inferior cava,
Coronary vein,

Foramina Thebesii,

Auriculo-ventricular.

Eustachian valve,

Coronary valve.

Annulus ovalis,

Fossa ovalis.

Tuberculum Loweri,
Musculi pectinati.

The Superior vena cava returns the blood from the upper half of the body, and opens into the upper and back part of the auricle.

The Inferior vena cava returns the blood from the lower half of the body, and opens through the lower and posterior wall, close to the partition between the auricles (septum auricularum). The direction of these two vessels is such, that a stream forced through the superior cava would rush towards the auriculoventricular opening. In like manner, a jet issuing from the inferior cava would dash its stream against the septum auricularum; this is the proper direction of the two currents during foetal life.

The Coronary vein returns the venous blood from the substance of the heart; it opens into the auricle between the inferior cava and auriculo-ventricular opening, under cover of the coronary valve.

The Foramina Thebesii' are minute pore-like openings of small veins (venæ minima) which issue directly from the muscular structure of the heart, without entering the venous current. These openings are also found in the left auricle,

1 Adam Christian Thebesius. His description of the openings now known by his name is contained in his "Dissertatio Medica de Circulo Sanguinis in Corde," 1708.

and in the right and left ventricles, but, in the latter, are generally believed to be mere cæcal depressions.

The Auriculo-ventricular opening is the large opening of communication between the auricle and ventricle.

The Eustachian' valve is a part of the apparatus of foetal circulation, and serves to direct the placental blood from the inferior cava, through the foramen ovale into the left auricle. In the adult it is a mere vestige and imperfect, though sometimes it remains of large size. It is formed by a fold of the lining membrane of the auricle, containing some muscular fibres, is situated between the aperture of the inferior cava and the auriculo-ventricular opening, and is generally connected with the coronary valve.

The Coronary valve is a semilunar fold of the lining membrane, stretching across the mouth of the coronary vein, and preventing the reflux of blood in the vein during contraction of the auricle.

ANATOMY OF THE HEART; RIGHT SIDE. 1.

Cavity of right auricle. 2. Appendix auricu!æ, in its cavity are seen the musculi pectinati. 3. Superior vena cava, opening into the upper part of right auricle. 4. Inferior vena cava. 5. Fossa ovalis; the prominent ridge surround. ing it is the annulus ovalis. 6. Eustachian valve. 7. Opening of the coronary vein. 8. Coronary valve. 9. Entrance of the auriculo-ventricular opening. Between the figures 1 and 9, two or three foramina Thebesii are seen. a. Right ventricle. b, c. Cavity of right ventricle, on the walls of which the columnæ carnea are seen; e is placed in the channel leading upwards to the pulmonary artery, d. e, f. Tricuspid valve; e is placed on the anterior curtain, ƒ on the right curtain. g. Long columna carnea, to the apex of which the anterior and right curtain are connected by chorda tendines. h. The "long moderator band." i. The two columnæ carnea of the right curtain. k. Attachment by chorda tendineæ of the left limb of the anterior curtain. 1, L. Chorda tendineæ of the "fixed curtain" of the valve. m. Valve of the pulmonary artery. The letter of reference is placed on the inferior semilunar segment. n. Apex of left appendix auricula. o. Left ventricle. p. Ascending aorta. q. Its transverse portion, with the three arterial trunks which arise from the arch. r. Descending aorta.

The Annulus oralis is situated on the septum auricularum, opposite the termination of the inferior cava. It is the rounded margin of the septum, which occupies the place of the foramen ovale of the foetus.

The Fossa ocalis is an oval depression corresponding with the foramen ovale

1 Bartholomew Eustachios, born at San Severino, in Naples, was Professor of Medicine in Rome, where he died in 1579. He was one of the founders of modern anatomy, and the first to illustrate his works with good engravings on ecpper.