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floor is partly formed by Rhomboideus major. If the scapula be drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for ausculation. The space is therefore known as the triangle of ausculation.

FIG. 1215– The left side of the thorax. (See enlarged image)

Mamma.—The size of the mamma is subject to great variations. In the adult nulliparous female, it extends vertically from the second to the sixth rib, and transversely from the side of the sternum to the midaxillary line. In the male and in the nulliparous female the mammary papilla is situated in the fourth interspace about 9 or 10 cm. from the middle line, or 2 cm. from the costochondral junction.

6. Surface Markings of the Thorax

Bony Landmarks.—The second costal cartilage corresponding to the sternal angle is so readily found that it is used as a starting-point from which to count the ribs. The lower border of the Pectoralis major at its attachment corresponds to the fifth rib; the uppermost visible digitation of Serratus anterior indicates the sixth rib.

The jugular notch is in the same horizontal plane as the lower border of the body of the second thoracic vertebra; the sternal angle is at the level of the fifth thoracic vertebra, while the junction between the body and xiphoid process of the sternum corresponds to the fibrocartilage between the ninth and tenth thoracic vertebræ.

The influence of the obliquity of the ribs on horizontal levels in the thorax is well shown by the following line. “If a horizontal line be drawn around the body at the level of the inferior angle of the scapula, while the arms are at the sides, the

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