Experiment 213.  Hold a pencil vertically about twelve inches from the nose, fix it with both eyes, close the left eye, and then hold the right index finger vertically, so as to cover the lower part of the pencil.  With a sudden move, try to strike the pencil with the finger.  In every case one misses the pencil and sweeps to the right of it.

  Experiment 214. To illustrate imperfect judgment of direction.  As
  the retina is spherical, a line beyond a certain length when looked at
  always shows an appreciable curvature.

  Hold a straight edge just below the level of the eyes.  Its upper margin
  shows a slight concavity.

Surface Anatomy and Landmarks.

In all of our leading medical colleges the students are carefully and thoroughly drilled on a study of certain persons selected as models.  The object is to master by observation and manipulation the details of what is known as surface anatomy and landmarks.  Now while detailed work of this kind is not necessary in secondary schools, yet a limited amount of study along these lines is deeply interesting and profitable.  The habit of looking at the living body with anatomical eyes and with eyes at our fingers’ ends, during the course in physiology, cannot be too highly estimated.

In elementary work it is only fair to state that many points of surface anatomy and many of the landmarks cannot always be defined or located with precision.  A great deal in this direction can, however, be done in higher schools with ingenuity, patience, and a due regard for the feelings of all concerned.  Students should be taught to examine their own bodies for this purpose.  Two friends may thus work together, each serving as a “model” to the other.

To the following syllabus may be added such other similar exercises as ingenuity may suggest or time permit.

Syllabus.

I. Bony Landmarks.

1.  The occipital protuberance can be distinctly felt at the back of the head.  This is always the thickest part (often three-quarters of an inch or more) of the skull-cap, and is more prominent in some than in others.  The thinnest part is over the temples, where it may be almost as thin as parchment.

2.  The working of the condyle of the lower jaw vertically and from side to side can be distinctly felt and seen in front of the ear.  When the mouth is opened wide, the condyle advances out of the glenoid cavity, and returns to its socket when the mouth is shut.  In front of the ear, lies the zygoma, one of the most marked and important landmarks to the touch, and in lean persons to the eye.

3.  The sliding movement of the scapula on the chest can be properly understood only on the living subject.  It can move not only upwards and downwards, as in shrugging the shoulders, backwards and forwards, as in throwing back the shoulders, but it has a rotary movement round a movable center.  This rotation is seen while the arm is being raised from the horizontal to the vertical position, and is effected by the cooperation of the trapezius with the serratus magnus muscles.