Interesting examples of monaural stethoscopes that have a narrow oval chest end which was intended to examine the chest in between the ribs so as to better auscultate the lungs. On the left is a completely solid model, circa 1850. On the right is a similar version, but with the central hole bored throughout the stethoscope, circa 1840. Note the photo which shows the chest ends of the stethoscopes with and without the hole.