In the absence of a craniometer, measurements may be taken with calipers, the arms of which are curved like the ordinary pelvimeters used in obstetrics (see [Fig. 31]), and a graduated steel tape.
The following are the principal measurements:
1. Maximum antero-posterior diameter, which is obtained by applying one arm of the instrument above the root of the nose just between the eyebrows and sliding the other arm over the vault of the skull till it reaches the occiput. The distance between the two arms furnishes the maximum longitudinal diameter.
2. The maximum transverse diameter or breadth of the skull is measured by placing the arms of the calipers, one on each side of the head on the most prominent spot.
3. The antero-posterior curve is obtained by fixing the graduated tape at zero on the root of the nose (on the fronto-nasal suture) and passing it over the middle of the forehead, vertex, and occiput to the external occipital protuberance.
4. The transverse, or biauricular curve is obtained by applying the steel tape at zero to a point just above the ear, and carrying it over the head in a vertical direction till it reaches the corresponding point on the other side.
5. The maximum circumference is obtained by encircling the head with the steel tape, touching the forehead immediately above the eyebrows, the occiput at the most prominent point, and the sides of the head more or less at the level, where the external ear joins the head, according to whether the position of the occipital protuberance is more or less elevated. (See [Figs. 32], [33].)
6. The cranial capacity is obtained by adding together these five measurements, the antero-posterior diameter, maximum transverse diameter, antero-posterior curve, transverse curve, and maximum circumference. For a normal male the capacity is generally 92 inches (1500 c.c).