Obstetrics for Nurses

by Charles B. Reed

Fig. 21.—Fœtal skulls showing sutures. Note the differences between the anterior and posterior fontanelles. (Eden.)

Fig. 22 A.—Child’s head at term (from side), showing diameter. (American Text Book.)

Fig. 22 B.—The child’s head at term (from above), showing diameters and fontanelles. (American Text Book.)

The fœtal skull at maturity (at term) is still incompletely ossified. The bones are thin and pliable and separated at their edges by intervals of unossified membrane which form the sutures and fontanelles. Thus the skull is compressible to a slight degree and capable of much change in shape. It can be measurably moulded by the uterine contractions to suit the pelvis.

In front, the two coronary sutures meet the frontal and sagittal sutures to produce a kite-shaped figure, called the large or anterior fontanelle, or the bregma. Behind, the lambdoidal suture meets the sagittal suture to form the small or posterior fontanelle.

The large fontanelle is made up of four bones and four angles; the small, of three bones and three angles, and are usually easy to differentiate. Furthermore, the difference between these fontanelles is of great importance in labor, since by it the observer is enabled to determine the position of the head. In America, the shape of the head is that of an ovoid with the long diameter anteroposterior (Dolico-cephalic). Thus it happens that when the head is completely flexed, the smallest diameters are presented for delivery.

The important diameters of the head, with their measurements and names, are as follows: