Describe the Heart. It is a hollow muscular organ, conoidal in shape, placed obliquely in the chest between the lungs, base upwards, apex towards the left and front, corresponding to the interspace between the 5th and 6th costal cartilages, one inch inside of and two inches below the left nipple. In the adult its size is about 5 inches by 31⁄2 by 21⁄2, and from 8 to 12 oz. in weight.

What are the Cavities of the Heart? They are 4 in number, an auricle and a ventricle on each side of the heart, separated by a longitudinal muscular septum, and indicated on the external surface of the organ by grooves, named, from their contiguous cavities, as the Auriculo-ventricular Groove transversely, and the Inter- Ventricular Groove longitudinally.

Describe the Right Auricle. It is larger than the left, can hold about 2 fluidounces, its walls being about 1 line in thickness. It receives the venous blood by the superior and inferior vena cava and the coronary sinus, and presents interiorly the following points for examination:

Appendix Auricula, a conical pouch projecting from the auricle to the front and left, its margins being dentated.

Openings of the superior and inferior vena cava and the coronary sinus, the latter having a valve in two segments.

Foramina Thebesii, several minute orifices, the mouths of veins from the substance of the heart.

Tubercle of Lower, a very small projection on the right wall, supposed to influence the direction of the blood-current.

Eustachian Valve, at the anterior margin of the inferior vena cava; large in the foetus, to direct the blood to the foramen ovale.

Fossa Ovalis, a depression on the inner wall, and the situation of the foramen ovale in the foetus.

Annulus Ovalis, the oval margin of the fossa ovalis.

Musculi Pectinati, muscular columns on the inner surface of the appendix and the inner wall of the auricle.

Auriculo-ventricular Opening, communicates with the right ventricle, is oval, about an inch broad, surrounded by a fibrous ring, and is guarded by the tricuspid valve.

Describe the Right Ventricle. Its form is conical, its cavity containing about 2 fluidounces, its apex above the apex of the heart, and it presents interiorly the following, viz.—

Tricuspid Valve, consists of 3 triangular segments connected by their bases with the auriculo-ventricular orifice, and by their sides with each other, the largest being on the left side.

Chorda Tendina, delicate tendinous cords which connect the margins and lower surfaces of the tricuspid valve with the columnæ.

Columna Carnea, muscular columns projecting from the surface of the ventricle, of which 3 or 4, called Columna Papillares, give attachment to the chordæ tendinæ.

Semilunar Valves, are 3 in number, and guard the orifice of the pulmonary

artery, each about the middle of its free margin has a fibro-cartilaginous nodule, the Corpus Arantii, which more perfectly closes the orifice. Opening of the Pulmonary Artery, at the superior and internal angle of the ventricle, the Conus Arteriosus. It is circular in form, surrounded by a fibrous ring, and is guarded by the semilunar valves.

Sinuses of Valsalva, are 3 pouches, one behind each valve, between it and the commencement of the pulmonary artery.

Describe the Left Auricle. Its walls are about 11⁄2 lines in thickness, its capacity rather less than 2 fluidounces, has an appendix auriculæ, and receives the arterialized blood from the lungs. It presents the following internally :

Openings of the Pulmonary Veins, are 4 in number, sometimes 3, as the two left veins frequently end in a common opening.

Left Auriculo-ventricular Opening, is smaller than the right one.
Musculi Pectinati, on the inner surface of the appendix.

Depression, corresponding to the fossa ovalis in the right auricle.

Describe the Left Ventricle.

It is longer, thicker, and more conical than the right, projecting towards the posterior aspect. Its wallsa are the thickest of those in the heart, being twice as thick as those of the right ventricle. Its interior presents the following:

Aortic Opening, is small and circular, placed in front and to the right of the auriculo-ventricular, a segment of the mitral valve being between them. It is surrounded by a fibrous ring, and guarded by semilunar valves.

Mitral Valve,c consists of two

unequal-sized segments, and is

FIG. 53.

attached to the fibrous ring which surrounds the auriculo-ventricular opening. Its margins are connected with the ventricular walls by Chorda Tendinad and Musculi Papillares.

Semilunar Valves, guard the aortic orifice, and are larger and stronger than those on the right side.

Sinus Aortici, or sinus of Valsalva, a pouch between each valve and the beginning of the aorta.

Columna Carnea,e are smaller and more numerous than on the right side; the Musculi Papillares are but two in number.

Describe the Structure of the Heart. The muscular fibres take origin from the four fibrous rings at the auriculo-ventricular and aortic openings. The fibres of the auricles are arranged in two layers, a superficial and a deep one, the latter having looped fibres and annular fibres. In the ventricles the fibres are superficial and deep, the latter being arranged circularly, the former spirally, coiling inwards at the apex of the heart into a whorl-like form, the

vortex.

THE ARTERIES.

What are the Arteries? Cylindrical vessels which carry arterial blood to the body from the heart. Those going to the lungs with the returning veins, form the Lesser or Pulmonic Circulation. The aorta with its branches and the returning veins, constitute the Greater or Systemic Circulation. The arteries anastomose or communicate freely with each other everywhere throughout the body, permitting the establishment of collateral circulations.

Describe the Structure of the Arteries. They are dense, very elastic, preserving their cylindrical form, and are composed of 3 coats, an Internal or serous; a Middle, which is of muscular and elastic tissue; and an External, of connective tissue. They are generally included in a fibro-areolar investment, the Sheath, which also encloses the accompanying veins. The larger arteries are nourished by the Vasa Vasorum, blood-vessels which ramify in the external and middle coats; and are supplied with nerves, the Vaso-motor, derived from both the sympathetic and cerebro-spinal systems, and forming intricate plexuses on the larger trunks.

What are the Capillaries? Minute vessels forming a network throughout the tissues of the body between the terminating arteries and the commencing veins. Their average diameter is about the gooo of an inch, and their walls consist of a transparent homogeneous membrane continuous with the innermost layer of the arterial and venous walls.

[In the following pages, main branches are in italics, sub-branches in Roman.] Describe the Aorta. It is the main trunk of the systemic arteries, commencing at the aortic opening of the left ventricle of the heart, arching backwards over the roof of the left lung into the thorax, where it descends on the left of the spinal column, and after passing through the aortic opening in the diaphragm, it terminates in the right and left common iliac arteries opposite

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the 4th lumbar vertebra. It is divided into the arch, the thoracic aorta, and the abdominal aorta; and the arch is subdivided into the ascending,5 transverse, and descending portions. The upper border of the arch is generally situated about an inch below the upper margin of the sternum. The branches of the aorta are,From the Arch,-2 Coronary. Left Common Carotid.10

Describe the Coronary Arteries. They are 2 in number, a right and a left, arise from the aorta behind the semilunar valves and run in the vertical grooves of the heart, the left artery in front, to supply the tissue of that organ.

Describe the Innominate. It arises from the summit of the arch of the aorta, is 11⁄2 inch long, and divides behind the right sterno-clavicular joint into the Right Common Carotid and Right Subclavian, these arteries on the left side of the body arising directly from the arch of the aorta.10 11 It sometimes sends off a Middle Thyroid (artery of Neibauhr) which may arise directly from the arch of the aorta. The innominate is sometimes absent, and not infrequently varies in length from an inch to two or more.

Inferior Mesenteric.

8 Lumbar.

Sacra Media.

2 Common Iliac.

Describe the Common Carotid. Arising differently (see above), the two carotids are similarly described, except that the left is longer and deeper than the right one. Their course is indicated by a line drawn from a point midway between the angle of the lower jaw and the mastoid process to the sterno. clavicular articulation. At the lower part of the neck they are separated only by the width of the trachea, and they are each contained in a sheath of the deep cervical fascia with the internal jugular vein externally and the pneumogastric nerve between the artery and vein. On the front of the sheath lies the descendens noni nerve (descending branch of the 9th or hypoglossal). The artery lies beneath the inner border of the sterno-cleido-mastoid muscle, and is crossed about its middle by the omo-hyoid muscle and the middle thyroid vein.

It is also crossed above by the facial, lingual, and superior thyroid veins, below by the anterior jugular vein, and on the left side often by the internal jugular vein. It bifurcates, at the level of the upper border of the thyroid cartilage, into the External and Internal Carotids, of which the internal is the most remote from the median line.

Name the Branches and Sub-branches of the External Carotid Artery.2 (Fig. 55.) It has 8 branches, as follows, viz.—

Superior Thyroid, arising below the greater cornu of the hyoid bone.

Muscular.

Glandular.

Hyoid.

Superficial Descending.

Superior Laryngeal.
Crico-thyroid.

Ranine.

Lingual, under the hyo-glossus muscle to the tongue.
Hyoid. Dorsalis Linguæ. Sublingual.

Facial, crosses the lower jaw at the anterior angle of the masseter.

Inferior or Ascending Palatine.

Tonsillar.

Submaxillary.

Submental.

Muscular.

Inferior Labial.

2 Coronary.89
Lateralis Nasi.
Angular.