Duval's artistic anatomy

The skeleton of the head is formed of two parts intimately united to each other: one above and behind, formed for the most part of flat bones, simple in form, and called the cranium, containing the brain: the other below and in front, consisting of numerous bones, complex in shape, and constituting the bony structure of the face. The facial bones form the boundaries of the cavities which lodge the principal organs of sense and the apparatus of mastication.

The cranium.—The cranium forms an egg-shaped box with its long axis directed from before backwards. It may be examined from its base, which we need not study here, or from above or from the side. The bones which enter into its construction are eight in number, viz. the sphenoid in the base and side wall, the occipital behind, the frontal in front, the two parietal above, and the two temporal bones on the sides.

The occipital bone (3, Fig. 56) forms the whole posterior part of the base and vault of the skull. The bone possesses two distinct parts, inferior and superior. The inferior part is more or less horizontal, and is pierced by a large foramen (foramen magnum) through which the cavity of the cranium communicates with that of the vertebral canal. In front of this foramen is the basilar process of the occipital bone; upon each side are the occipital condyles, by which the skull articulates with the vertebral column—namely, with the lateral masses of the atlas (pp. 31, 32). The superior part (3, Fig. 56), called the squamous or shell-shaped portion of the bone, is more or less triangular in form, with the apex directed upwards. Its borders are hollowed out into numerous irregular denticulations, which work in with similar denticulations on the posterior borders of the parietal bones (7, Fig. 56); and assist in forming the lambdoidal suture. The external or posterior surface is crossed about its middle by a semicircular crest (the superior curved lines) of which the centre forms a prominence called the external occipital protuberance. This prominence is placed below the most projecting point of the back of the skull. The superior curved lines separate the outer or posterior surface of the occipital bone into an upper smooth part, belonging to the vault, which is covered by the scalp, and a lower rough surface, to which the muscles of the neck are attached.

The parietal bones (2 and 13, Fig. 56) are placed on each side of the vault of the skull in front of the occipital bone. Quadrilateral in shape, each bone presents four denticulated borders, of which the superior articulates with the parietal of the opposite side, the posterior with the occipital (7, Fig. 56), the anterior with the frontal (6), and the inferior, which is concave (8, Fig. 56), with the temporal and (slightly) with the sphenoid bone. The parietal bone presents two points for notice on its external surface—1, near its centre a projection called the parietal eminence, better marked in young subjects than in the adult, which represents the place where the ossification of the bone commences; 2, below this prominence a curved line, the temporal ridge, slightly rough (13, Fig. 56), which limits the temporal fossa and gives attachment to the temporal fascia.

The frontal bone, a single bone (1, Fig. 56), like the occipital, presents, like it, a vertical and a horizontal part. The latter belongs to the base of the skull and to the face (9, 9, Fig. 57), and forms the roof of the cavity of the orbit (see below). The vertical part forms the anterior and superior wall of the cranium. It has a rounded superior border (11, Fig. 57) which articulates by its denticulated edge with the parietal bones and forms the coronal suture (6, Fig. 56). The anterior superficial surface forms the forehead, and upon it we have to notice the following points:—1, the frontal eminences (1, 1, Fig. 57), better marked in young subjects and in females than in the adult male; 2, below these, the superciliary ridges (2, 2, Fig, 57), which are directed obliquely downwards and inwards, to end in two prominent bosses called the nasal eminences. These prominences are best marked in the adult, and owe their prominence to the fact that the thickness of the bone is hollowed out in this situation into two cavities called the frontal sinuses, which become more developed as the subject advances in age; 3, at the lower border of this part of the bone are the supra-orbital arches (4, 4, Fig. 57), at the margin of the orbit. Curved, with the concavity downwards, each of these arches forms on the outer side an external angular process (6, 6, Fig. 57), which articulates with the malar, or cheek-bone (15, Fig. 56), and on the inner side an internal angular process (5, 5, Fig. 57) which articulates with the nasal process of the upper jaw. Between the two internal angular processes is a median rough space called the nasal notch (7, Fig. 57), into which are received the nasal bones (22, Fig. 56). Each supra-orbital arch presents, at the junction of its middle and inner thirds, a small notch called the supra-orbital notch (Fig. 57).

The temporal bones, one on each side of the skull (4, 11, and 31, Fig. 56), are very complex in shape, but we shall study here only one portion. Each temporal bone is composed of two parts, one belonging to the base, and another belonging to the lateral wall of the skull; the part belonging to the base forming a pyramidal mass of very dense bone, called the petrous portion, which contains the delicate organs of the internal ear; while the part belonging to the lateral wall of the skull (4, Fig. 56) rises up as an irregular osseous disc from the base of the petrous portion of the bone. An orifice, the external auditory meatus which leads into the petrous bone, is found about its centre (31, Fig. 56). Taking this orifice of the auditory canal as a centre, we find on the external surface of the temporal bone—1, behind the auditory canal the mastoid portion of the bone (33, Fig. 56), which articulates with the parietal and occipital bones, and is prolonged downwards as a conical process in the shape of a nipple (μαστός, a nipple) called the mastoid process; 2, above the auditory canal, the squamous portion of the temporal bone (4, Fig. 56), a shell-like bone with a rounded border articulating with the inferior border of the parietal bone (8, Fig. 56). In front is a process (20, Fig. 58) which is directed horizontally towards the face and joins the malar bone (16, Fig. 56). This process, connecting the cranium with the face, is called the zygomatic process (ζυγός, a yoke), and it forms with the corresponding part of the malar bone the zygomatic arch. The zygomatic process rises from the temporal bone by two roots (Fig. 57), of which one sweeps backwards above the orifice of the external auditory canal and helps to form the temporal ridge; the other extends as a rounded ridge transversely inwards towards the base of the skull, and as the eminentia articularis, forms the anterior limit of the glenoid cavity, into which the condyle of the lower jaw is received. Finally, below the auditory canal, the temporal bone gives origin to the styloid process (32, Fig. 56), long and slender, which gives attachment to certain ligaments and muscles of the neck.

The sphenoid bone is one of the most important in the construction of the cranium, although as it chiefly occupies the middle of the base of the skull, it is not very obvious on the surface. It is the great wing of the sphenoid bone which assists in the formation of the temporal fossa.

The bones of the cranium articulate with one another by denticulated borders, to which the name of sutures is given. As the artist needs to study the skull not only with regard to its superficial form, but also as an object which figures frequently as an accessory in still-life compositions, and as a true representation of these sutures contributes to give to the skull its exact physiognomy, we must not leave the subject without carefully pointing them out. It is necessary for our purpose to examine the skull on its upper and its lateral surfaces.

The upper surface of the skull presents a suture in the middle line, antero-posterior and inter-parietal, called the sagittal suture. Behind, on a level with the superior angle of the occipital bone (7, Fig. 56), this median suture becomes continuous with the occipito-parietal suture to which the name of the lambdoid suture is given-because it resembles the form of a Greek lambda (Λ). In front, the sagittal suture is met by the parieto-frontal suture (6, Fig. 56), which forms a curved line, to which has been given the name of the coronal suture.

On examining the skull on one of its lateral surfaces, we see that the sutures form in this situation a more complex design, because of the articulations of the bones entering into the formation of the temporal fossa (5, 10, 11, 12, Fig. 56). This fossa is formed by the parietal, squamous portion of the temporal, frontal, and great wing of the sphenoid bones. It is limited: below by the zygomatic arch (malar and temporal), and above by the curved line of the temporal ridge, which marks the temporal, parietal, and frontal bones. The suture formed within the fossa, at a point called the pterion, is roughly or -shaped, and is occasioned by the contiguous articulations of the parietal, sphenoid, frontal, and squamous portion of the temporal bones.

We have said that the general form of the skull is egg-shaped, with its greater extremity behind. It is, however, a common observation that the skull may differ remarkably from what may be termed the normal shape. It may be excessively high, or low; excessively prolonged backwards or forwards, or the reverse. One of the best-marked and constant variations is in the ratio of width to length, from which the cephalic index is derived. This may be an individual peculiarity: for instance, of two brothers, one may be round-headed, the other long-headed. Or it may be a racial character: for example, the black races are long-headed, the yellow races are round-headed, and the white races have a cephalic index which may be one or the other, or intermediate between the two extremes.

The cephalic index (index of breadth of the skull) is an important term in physical anthropology.

As we have previously explained, respecting the proportions of the arm and forearm (brachial index, page 100), we understand by the name of index the number which indicates the proportion between a short and a greater length, the latter being considered as equal to 100—that is to say, the figures obtained by direct measurement being reduced to a decimal proportion. We find that in certain skulls the transverse diameter is relatively very short, seeing that it is represented by an index of 75 or less; and such skulls are known as dolichocephalic (δολιχός, lengthened; κεφαλή, head). Others present a transverse diameter which approaches the antero-posterior, since it is represented by an index of 80 or more, the antero-posterior measurement being 100. This cephalic index of 80 or more is called brachycephalic (βραχύς, short). Between these two types are the heads of intermediate form called mesaticephalic, of which the cephalic index is from 75 to 80. The importance of dolichocephalic, mesaticephalic, and brachycephalic types of skull in relation to racial characters has no doubt been exaggerated; but the fact remains that certain races are dolichocephalic, and that certain other races are brachycephalic. A greater difficulty arises in regard to mesaticephalic skulls, which are, after all, in a sense only “averages,” and which, occurring as they do so commonly in the Indo-European race, suggest that either they are due to individual peculiarity or to the mingling of racial characters—in either case weakening the value of skull measurements in the investigation of races.