The bony landmarks of the head will first be considered, followed by a separate description of the cranium and the face.
Bony landmarks. - These should be studied with the aid of a skull, as well as on the hving subject. Beginning in front is the nasion, a depression at the root of the nose, and immediately above it, the glabella, a slight prominence joining the two supracihary arches. These points mark the remains of the frontal suture, and the junction of the frontal, nasal, and superior maxillary bones and one of the sites of a meningocele. In the middle line, behind, is the external occipital protuber- ance, or inion, the thickest part of the vault, and corresponding internally with the meeting-point of six sinuses. A line joining the inion and glabella corresponds to the sagittal, and occasionally the frontal, suture, the falx cerebri, the superior sagittal sinus, widening as it runs backward, and the longitudinal fissure of the brain. From the inion the superior nuchal hues pass laterally toward the upper and back part of the base of the mastoid processes, and indicate the first or so- called horizontal part of the transverse (lateral) sinus.
This vessel usually presents a varying curve upward and runs in the tentorium. The second or sigmoid portion turns downward on the inner surface of the mastoid, then forward, and lastly downward again to the jugular foramen, thus describing the double curve from which this part takes its name. In the jugular foramen the vessel occupies the posterior compartment; its junction with the internal jugular is dilated and forms the bulb. A line curved downward and forward from the upper and back part of the base of the mastoid, reaching two-thirds of the way down toward the ape.x, will indicate the second part of the sinus. The spot where it finally curves inward to the bulb would be about 1.8 cm. (J in.) below and behind the meatus. The two portions of the transverse sinus meet at the asterion laterally; at the entry of the superior petrosal sinus medially. The right transverse sinus, the larger, is usually a continua- tion of the superior sagittal sinus, and, therefore, receives blood chiefly from the cortex of the brain; the left, arising in the straight sinus, drains the interior of the brain and the basal ganglia. Each transverse sinus receives blood from the temporal lobe, the cerebellum, diploe, tympanic antrum, internal ear, and two emissary veins, the mastoid and posterior condylar.
About 6.2 cm. (2.5 in.) above the external occipital protuberance is the lambda, or meeting of the sagittal and lambdoidal sutures (posterior f ontanelle, small and triradiate in shape) . It is useful to remember, as guides on the scalp to the above two important points, that the lambda is on a level with the supraciUary ridges, and the external occipital protuberance on one with the zygomatic arches.
Below the external occipital protuberance, between it and the foramen magnum, an occip- ital, the commonest form of cranial meningoceles, makes its appearance. It comes through the median fissure in the cartilaginous part of the squamous portion of the bone.
The point of junction of the occipital, parietal, and mastoid bones, the asterion, is placed about 3.7 cm. (1.5 in.) behind and 1.2 cm. (0.5 in.) above the center of the auditory meatus. It indicates the site of the posterior lateral fontanelle and just below it the superior nuchal line terminates. The bregma, or junction of the coronal, sagittal, and, in early life, the frontal suture (anterior f on- tan elle, large and lozenge-shaped), lies just in front of the center of a line drawn transversely over the cranial vault from one pre-auricular point to the other. The bregmatic fontanelle normally closes before the end of the second year. The lambdoid fontanelle is closed at birth. The pterion, or junction of the frontal and sphenoid in front, parietal and squamous bones behind, lies in the temporal fossa, 3.7 to 5 cm. (1.5 to 2 in.) behind the zygomatic process of the frontal, and about the same distance above the zygoma. This spot also gives the position of the trunk and the anterior and larger division of the middle meningeal artery, the Sylvian point and divergence of the limbs of the lateral (Sylvian) fissure, the insula (island of Reil), and middle cerebral artery. It, further, corresponds to the anterior lateral fontanelle. On the side of the skull the zygomatic arch, the temporal ridge, and external auditory meatus need atten- tion. That important landmark, the zygomatic arch, wide in front where it is formed by the zygomatic (malar), narrowing behind where it joins the temporal, gives off here three roots, the most anterior marked by the eminentia articularis, in front of the mandibular (glenoid) fossa, the middle behind this joint, while the posterior curves upward and backward to be continuous with the temporal ridge. Within the zygomatic arch lie two fossae separated by the infra-temporal (ptery- goid) ridge : above is the temporal, with the muscle and deep temporal vessels and nerves; below is the infra-temporal or zygomatic fossa, with the lower part of the temporal muscle, the two pterygoids, the internal maxillary vessels, and the man- dibular division of the fifth. To the upper border of the zygomatic arch is attached the temporal fascia, to its lower, the masseter. Its upper border marks the level of the lower lateral margin of the cerebral hemisphere. A point corresponding to the middle root of the zygoma, immediately in front of the tragus, and on a level with the upper border of the bony meatus, is called the pre-auricular point. Here the superficial temporal vessels and the auriculo-temporal nerve cross the zygoma, and a patient 's pulse may be taken by the anaesthetist. The lower end of the central (Rolandic) fissure lies 5 cm. (2 in.) vertically above this point. The temporal ridge, giving origin to the temporal fascia, starts from the zygomatic proc- ess of the frontal, and becoming less distinct, curves upward and backward over the lower part of that bone, crosses the coronal suture, traverses the parietal bone, curving downward and backward to its posterior inferior angle. Here it passes on to the temporal, and passing forward over the external auditory meatus, is continuous with the posterior root of the zygoma. Below the root of the zygoma will be felt the temporo-mandibular joint, and when the mouth is opened, the con- dyle will be felt to glide forward on the eminentia articularis, leaving a well-marked depression behind.
The external auditory meatus, measured from its opening on the concha to the membrane, is about 2.5 cm. (1 in.) in length; if from the tragus, 3.7 cm. (1.5 in.). Its long axis is directed medially and a little forward with a slight convex curve upward, most marked in its center. Between the summit of this curve and the membrane is a sUght recess in which foreign bodies may lodge. The lumen is widest at its commencement, narrowest internally. To bring the cartilaginous portion in line with the bony, the pinna should be drawn well upward and back- ward. In the bony portion the skin and periosteum are intimately blended, thus accounting for the readiness with which necrosis occui's. The sensibility of the meatus is explained by the two branches sent by the auriculo-temporal nerve. The fact that the deeper part is supplied by the auricular branch of the vagus explains the vomiting and cough occasionally met with in affections of the meatus.
The anterior inferior angle of the parietal bone, and its great importance as a landmark, have already been noted. The posterior inferior angle of tliis bone (grooved by the transverse (lateral sinus) lies a httle above and behind the base of the mastoid, on a level with the roots of the zygoma. Just below and in front of the tip of the mastoid the transverse process of the atlas can be made out in a spare subject.
In front, the circumference of the bony orbit can be traced in its whole extent. The supraorbital notch lies at the junction of the medial and intermediate thirds of the supraorbital arch. When this notch is a complete foramen, its detection is much less easy. To its medial side the supratrochlear nerve and frontal arterd cross the supraorbital margin; like the supraorbital, this nerve and vessel lie, at first, in close relation with the periosteum. The frontal artery is one of the chief blood-supplies to flaps taken from the forehead. Owing to the paper6like thinness of the bones on the medial wall of the orbit, e. g., lacrimal, ethmoid, and body of sphenoid, and the mobihty of the skin, injuries which are possibly pene- trating ones, as from a slate-pencil, ferrule, etc., are always to be looked upon with suspicion. After a period of latency of symptoms, infection of the membranes and frontal abscess have often followed. Above the supraorbital margin is the supraciliary arch, and higher still the frontal eminence [tuber frontale].
The Skull, showing Kronlein's Method of Ckaniocerebral Topography.
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