The face (Fig. 168) is composed of fourteen bones, two being single, the inferior maxilla and vomer; and six being double, the superior max Ulm, the palate, the lachrymal, the nasal, the inferior turbinated and the molars.
The cranium (Fig. 169) is composed of eight bones. Four, the frontal, occipital, sphenoid and ethmoid, are single; and two, the parietal and temporal, are double.
The vault of the cranium is formed in front by the frontal bone, on the sides by the parietal and the squamous plate of the temporal, and behind by the occipital. The base is composed of the basilar portion of the occipital, the sphenoid, the ethmoid, and the petrous portion of the temporal. Whilst the bones of the base are firmly united to one an other, those of the vault of the skull arc separated from each other by considerable membranous intervals, and allow an amount of motion and overlapping which permits within limits a reduction in the size of the head, which is important at the time of birth.
These membranous spaces are the sutures and fontanelles; and, follow ing liudin, we will add to them the occipital hinge.
There are five the frontal, sagittal, lambdoid, and two temporo parietal. The first three only are of importance to the accoucheur, since they only can be appreciated by the touch.
The frontal or fronto-parietal suture separated the two parietals from the frontal; it runs transversely across the skull, and is cro..sed at its middle by the sagittal suture.
The sagittal or great suture runs from the root of the nose to the apex of the lambdoid suture. It is crossed by the frontal suture.
The occipito-parietal or lambdoid suture (4 of the Greeks), lies between the posterior borders of the parietals, and the ocipital. Its apex touches the posterior end of the sagittal suture, and its extremities end at the squamons plate of the temporal.
When the head is compressed in the pelvis, these sutures project instead of being gutter-shaped, from the sliding of the bones on each other.
The fontanelles are the membranous spaces where the sutures meet. We have: 1st. The Anterior or Great Fontanelle, or Bregma or Bregtnatic Fonla by the union of the fronto-parietal with the sagittal suture, it is of quadrangular shape, and has four angles and four borders. The
anterior angle is formed by the divergence of the two halves of the frontal, and the posterior angle by the uniting parietals; the two lateral angles are made by the divergence of the halves of the frontal from the parietal of the same side. The edges are formed by the borders of the frontal and the parietals. (Fig. 169.) Each angle is continuous with a suture, and this, together with its quadrangular shape, enables us always to distinguish it from one of the supplemental sutures, which are accidental, and smaller membranous spaces along the sagittal suture.
2d. The small or posterior or occipital fontanelle is situated at the point of junction of the sagittal and the lambdoidal sutures. It is triangular, and much smaller than the anterior fontanelle; its three angles are formed by the occipital and parietal bone. Velpeau has shown that in certain cases the occipital is, like the frontal, divided into two halves; but this posterior prolongation of the sagittal suture is always much shorter than the anterior one. (Fig. 169.) Budin has shown that between the basilar portion of the occipital and its squamous part, there is a sort of fibro-cartilaginous joint, permit ting movements of flexion and extension. It is rapidly ossified after birth.
Finally, at the extremities of the lambdoid suture are the two fontanelles of Gasser, which are covered by the soft parts so completely as not to fall under our observation as accoucheurs. (Fig. 169.) Diameters and Circumferences Of the distinguish antero posterior, vertical, and transverse diameters.
The antero-posterior diameters are: 1. The occipito-mental diameter, which, running from the occipi tal protuberance to the chin, measures 5.4 inches.
The occipito-frontal diameter, 0.F., extending from the occipital pro tuberance to the root of the nose, measures 4.6 inches.
3d. The sub-occipito-bregmatic, S.O.B., runs from the point of meeting of the occipital and the nucha, at the middle of the great fontanelle, at the level of the point where the sagittal and fronto-parietal sutures cross; it measures 3.8 inches.