Anatomy of the Human Body - Book XII Surface Anatomy and Surface Markings by Henry Gray
Various bony surfaces and prominences on the skull can be easily identified by palpation. The external occipital protuberance is situated behind, in the middle line, at the junction of the skin of the neck with that of the head. The superior nuchal line runs lateralward from it on either side, while extending downward from it is the median nuchal crest, situated deeply at the bottom of the nuchal furrow. Above the superior nuchal lines the vault of the cranium is thinly covered with soft structures, so that the form of this part of the head is almost that of the upper portion of the occipital, the parietal, and the frontal bones. The superior nuchal line can be followed lateralward to the mastoid portion of the temporal bone, from which the mastoid process projects downward and forward behind the ear. The anterior and posterior borders, the apex, and the external surface of this process are all available for superficial examination. The anterior border lies immediately behind the concha, and the apex is on a levelwith the lobule of the auricula. About 1 cm. below and in front of the apex of the mastoid process, the transverse process of the atlas can be distinguished. In front of the ear the zygomatic arch can be felt throughout its entire length; its posterior end is narrow and is situated a little above the level of the tragus; its anterior end is broad and is continued into the zygomatic bone. The lower border of the arch is more distinct than the upper, which is obscured by the attachment of the temporal fascia. In front, and behind, the upper border of the arch can be followed into the superior temporal line. In front, this line begins at the zygomatic process of the frontal bone as a curved ridge which runs at first forward and upward on the frontal bone, and then curving backward separates the forehead from the temporal fossa. It can then be traced across the parietal bone, where, though less marked, it can generally be recognized. Finally, it curves downward, and forward, and passing above the external acoustic meatus, ends in the posterior root of the zygomatic arch. Near the line of the greatest transverse diameter of the head are the parietal eminences, one on either side of the middle line; further forward, on the forehead, are the frontal eminences, which vary in prominence in different individuals and are frequently unsymmetrical. Below the frontal eminences the superciliary arches, which indicate the position of the frontal sinuses, can be recognized; as a rule they are small in the female and absent in children. In some cases the prominence of the superciliary arches is related to the size of the frontal sinuses, but frequently there is no such relationship. Situated between, and connecting the superciliary ridges, is a smooth, somewhat triangular area, the glabella, below which the nasion (frontonasal suture) can be felt as a slight depression at the root of the nose.
Below the nasion the nasal bones, scantily covered by soft tissues, can be traced to their junction with the nasal cartilages, and on either side of the nasal bone the complete outline of the orbital margin can be made out. At the junction of the medial and intermediate thirds of the supraorbital margin the supraorbital notch, when present, can be felt; close to the medial end of the infraorbital margin is a little tubercle which serves as a guide to the position of the lacrimal sac. Below and lateral to the orbit, on either side, is the zygomatic bone forming the prominence of the cheek; its posterior margin is easily palpable, and on it just above the level of the lateral palpebral commissure is the zygomatic tubercle. A slight depression, about 1 cm. above this tubercle, indicates the position of the zygomaticofrontal suture. Directly below the orbit a considerable part of the anterior surface of the maxilla and the whole of its alveolar process can be palpated. The outline of the mandible can be recognized throughout practically its entire extent; in front of the tragus and below the zygomatic arch is the condyle, and from this the posterior border of the ramus can be followed to the angle; from the angle to the symphysis the lower rounded border of the mandible can be easily traced; the lower part of the anterior border of the ramus and the alveolar process can be made out without difficulty. In the receding angle below the chin is the hyoid bone, and the finger can be carried along the bone to the tip of the greater cornu, which is on a level with the angle of the mandible: the greater cornu is most readily appreciated by making pressure on one side, when the cornu of the opposite side will be rendered prominent and can be felt distinctly beneath the skin.