second phalanges; action, flexes the lesser toes; nerve, internal plantar.

Abductor minimi digiti: origin, outer tubercle of the os calcis, the bone in front of both tubercles, plantar fascia, and intermuscular septum; insertion, with

4

Third layer.

the short flexor of the little toe into the outer side of the base of the first phalanx; action, abducts the little toe; nerve, external plantar.

Second layer.

Flexor accessorius: origin, by two heads, from the concave surface of the calcis and inferior calcaneo-navicular ligament, from the os calcis in front of the outer tubercle, and from the long plantar ligament; insertion, outer margin and upper and under surfaces of the tendon of the long flexor of the toes; action, modifies the oblique pull of the long flexor; nerve, external plantar.

Lumbricales: origin, tendons of the long flexor; insertion, expansion of the long extensor over the first phalanges; action, flex the first phalanx, extend the last two; nerves, the innermost lumbricalis by the internal, the three outer by the external plantar nerve.

Flexor brevis hallucis: origin, inner border of the cuboid and contiguous portion of the external cuneiform, and prolongation of the tibialis posticus tendon; insertion, inner and outer side of the base of the first phalanx of the great toe by two tendons, each containing a sesamoid bone, the inner tendon blending with that of the abductor hallucis, the outer with that of the adductor obliquus and the adductor transversus hallucis ; action, flexes the great toe; nerve, internal plantar.

Adductor obliquus hallucis: origin, tarsal extremities of the second, third, and fourth metatarsal bones and sheath of the tendon of the peroneus longus; insertion, with outer portion of

the short flexor into the outer side of the base of the first phalanx of the great toe; action, adducts the great toe; nerve, external plantar.

Adductor transversus hallucis: origin, inferior metatarsophalangeal ligaments of the three outer toes and transverse metatarsal ligament; insertion, with the adductor obliquus hallucis into the outer side of the first phalanx of the great toe; action, adducts the great toe; nerve, external plantar.

Flexor brevis minimi digiti: origin, base of the fifth metatarsal and sheath of the peroneus longus tendon; insertion, outer side of the base of the first phalanx of the little toe, often to the head of the fifth metatarsal; action, flexes and abducts the first phalanx; nerve, external plantar.

Fourth layer.

Dorsal interossei (four): origin, each by two heads from the adjacent sides of the metatarsal bones; insertion, tendinous into the bases of the first phalanges and aponeuroses of the common extensor; action, flexes the first phalanx, extends the last two, abducts toes from an imaginary line passing through the center of the second toe; nerves, external plantar and anterior tibial.

Plantar interossei (three): origin, single heads from the base and inner sides of the shaft of the third, fourth, and fifth metatarsal bones; insertion, inner sides of the bases of the phalanges and extensor aponeuroses of the same toes; action, flex and extend as above, and adduct the toes toward a line passing through the middle of the second toe; nerve, external plantar.

THE VASCULAR SYSTEM.

What is the pericardium?

A closed fibro-serous sac of conical form, its apex surrounding the great vessels for about two inches above their origin, its base downward, attached to the central tendon of the diaphragm. The outer fibrous coat is continued as tubular prolongations, lost upon the external coats of the roots of all the great vessels except the inferior vena cava, and is finally traceable as continuous with the deep layer of the cervical fascia ; the serous coat lines the sac, forming a parietal layer, and is reflected over the heart and great vessels, forming a visceral layer; its function is the secretion of a thin fluid in sufficient

amount to moisten the surfaces, thus lessening friction during the heart's movements.

Describe the heart and its position.

It is a hollow, conical muscle, with four distinct cavities, situated obliquely between the lungs, the base upward, backward, and to the right, the apex " (Fig. 101) downward, forward, and to the left, corresponding to the fifth intercostal space, three and a half inches from the middle line of the sternum. The upper limit of the heart is represented by a line passing from the lower border of the second left costal cartilage to the upper border of the third on the right side. The auriculoventricular groove is shown by a line drawn obliquely from the sternal end of the third left cartilage to the upper border of the sternal end of the seventh on the right side. The right border is represented by a line from the third right to the seventh right chondro-sternal articulation, arching outward one and a half inches from the middle line; the lower limit, by a line from the seventh right articulation to the apex in the fifth space; the left border, from the second left cartilage to the

apex.

The pulmonary valve is covered by the sternal end of the third left cartilage; the aortic valve is a little below and internal to this, behind the sternum, on a level with the third space, between the mid-sternal and left sternal lines. The auriculoventricular openings are lower than the arterial. The mitral is at the sternal end of the third left space (behind the sternal end of the fourth left costal cartilage, Quain). Draw a horizontal line between the two sternal ends of the fifth cartilages; where this line intersects the one marking the auriculo-ventricular groove is the spot indicating the tricuspid valve, behind the sternum.

Give the size and weight of the heart.

In adults it measures five inches long, three and one-half broad, and two and one-half thick; weighs in the male ten to twelve ounces, in proportion to the body 1 to 169; in females, eight to ten ounces, 1 to 149.

What are the four cavities of the heart called?

The right auricle and the right ventricle, the left auricle and the left ventricle, separated by a longitudinal septum—indi

cated externally in front and behind by the interventricular grooves dividing the heart into lateral halves, the right or venous heart, the left or arterial heart; an oblique auriculoventricular groove on the exterior corresponds to the division between the auricles and the ventricles.

Describe the right auricle.

Larger than the left auricle, with a capacity of about two fluid ounces; its walls are about one line thick; the venous blood is poured in by the superior and the inferior venæ cava and the coronary sinus; note the following points:

The sinus or atrium, the large quadrangular cavity between the two venæ cavæ; the appendix auriculæ, a conical pouch with dentated edge, projecting forward to the left over the root of the aorta; openings of the two venæ cave, also that of the coronary sinus", its orifice guarded by a semicircular fold called the coronary valve-sometimes two unequal segments are found; the tubercle of Lower, a small projection on the right upper wall directing blood from the superior cava toward the auriculo-ventricular opening, not marked in man; the foramina Thebesi, the mouths of numerous minute veins returning blood from the heart-muscle; openings of a few anterior cardiac veins; the semilunar Eustachian valve" between the anterior margin of the inferior vena cava and auriculo-ventricular opening-it is larger in the fetus, serving to direct the blood of the inferior cava through the foramen ovale; the fossa ovalis", an oval depression at the lower part of the auricular septum, the site of the oval foramen in the fetus; the annulus ovalis, the prominent margin of the fossa ovalis; the musculi pectinati, small prominent muscular columns running across the inner surface of the appendix and adjoining wall of the sinus; the oval auriculo-ventricular orifice, about one inch in diameter, communicating with the right ventricle, its margins formed by a fibrous ring covered by the lining membrane, and guarded by the tricuspid valve.

Describe the right ventricle.

It is triangular, with the apex downward, not quite reaching that of the heart, forming with the right auricle the anterior, rather than the right side of the heart; its capacity is about

three fluid ounces; it presents the following points for ex

amination :

Above is the conical prolongation called the conus arteriosus, from which opens the pulmonary artery placed to the left of the auriculo-ventricular orifice, which is surrounded by a fibrous ring; the pulmonary semilunar valves guard the pulmonary orifice; the tricuspid valve 5, 5, 5", formed of three triangular segments the largest on the left side-by a reduplication of the lining membrane with interposed fibrous tissue; the flaps are called the left, right, and posterior or septal; they are prevented from being forced into the auricle by the

Chorda tendinex", fine tendinous cords stretching from (1) the columnæ carnea to the attached margins of the leaflets, (2) to their centers, and (3) to their free margins.

The columna carnea", three varieties of muscular columns, (1) simple ridges, (2) bands attached by both extremities, and (3) two musculi papillares, muscular eminences from which arise the chordæ tendineæ. The anterior muscle is larger and more constant than the posterior, which may be represented by two or three smaller muscles.

The three pulmonary semilunar valves, two anterior, a right and a left, and one posterior, formed by a reduplication of the lining membrane with interposed fibrous tissue, with their free margins strengthened by a bundle of fibrous tissue, whose fibers radiate from a fibro-cartilaginous nodule-corpus Arantii-to all parts, except to two narrow lunated portions (lunulæ) on either side of the nodule, which are forced into contact when the valves are closed; above and behind each valve is a dilatation, the sinus of Valsalva.

Describe the left auricle.

Resembles the right in having a principal cavity or sinus and an appendix, but its walls are thicker, measuring about one and one-half lines. The following points should be studied:

The openings of the pulmonary veins, usually four in number, two emptying into the right and two into the left side; frequently the latter terminate by a common opening.

The oval auriculo-ventricular opening, surrounded by a fibrous ring, smaller than the right; the musculi pectinati fewer and smaller than on the right side; a depression over the site of the fossa ovalis of the right auricle.