1332 CLINICAL AND TOPOGRAPHICAL ANATOMY 



The point of junction of the occipital, parietal, and mastoid bones, the asterion, 

 is placed about 3 . 7 cm. (1| in.) behind and 1 . 2 cm. (| in.) above the centre of the 

 auditory meatus (fig. 1085). It indicates the site of the posterior lateral fon- 

 tanelle 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 fon- 

 tanelle, large and lozenge-shaped), lies just in front of the centre of a line drawn 

 transversely over the cranial vault from one pre-auricular point to the other (fig. 

 1090) . 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| to 2 in.) behind the zygomatic process of the frontal, and 

 about the same distance above the zygoma (fig. 1085). This spot also gives the 

 position of the trunk and the anterior and larger division of the middle meningeal 

 artery (fig. 1090), 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 zj^gomatic (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 Math 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 zygoina, 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^ in.). Its long axis is directea 

 medially and a little forward with a slight convex curve upward, most marked in its centre. 

 Between the summit of this curve and the membrane is a slight 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 occurs. The sensibility of the meatus is explained by 

 the two branches sent by the auriculo-temf)oral 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 t he meatus. 



The anterior inferior angle of the parietal bone, and its great importance as a landmark, 

 have already l)een noted. The posterior inferior angle of this bone (grooved by the transverse 

 (lateral) sinu.s) lies a little above and behind the base of the mastoici, on a level with the roots 

 of the zygoma (fig. 108.5). 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. 

 I'lie 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 

 cro.ss the supraorbital margin; like the supraorbital, this nerve and vessel lie, at 



