THE SKULL AS A WHOLE 101 



The sutures of the vertex are:— 



The metopic, which is, in most skulls, merely a median fissure in the frontal bone just 

 above the glabella; occasionally it involves the whole length of the bone. It is due to the 

 persistence of the fissure normally separating the two halves of the bone in the infant. ' 



The sagittal is situated between the two parietals, and extends from the bregma to the 

 lambda. 



The coronal lies between the frontal and parietals, and extends from pterion to pterion. 



The lambdoid is formed by the parietals and interparietal portion of the occipital. It 

 extends from aster ion to asterion. 



The occipital sutm-e is only present when the interparietal exists as a separate element 

 (figs. 70 and 71). 



The more important points are: — • 



The bregma, which indicates the situation of the frontal (greater) fontanelle, and marks 

 the confluence of the coronal, the sagittal, and, when present, the metopic sutures. 



The lambda, where the sagittal enters the lambdoid suture; it marks the situation of the 

 occipital (lesser) fontanelle. 



The obelion, a little anterior to the lambda, is usually indicated by a median or two lateral 

 foramina. 



(2) The Posterior Region 



Viewed from behind {norma occipitalis) the skull is somewhat pentagonal in 

 form. Of the five angles, the superior or median is situated in the line of the 

 sagittal suture; the two upper lateral angles coincide with the parietal eminences 

 and the two lower with the mastoid processes of the temporal bones. Of the 

 sides, four are somewhat rounded, and one, forming the basal line, running 

 between the mastoid processes, is flattened. 



The centre is occupied by the lambda, and radiating from this point are three sutures, 

 the sagittal, and the two parts of the lambdoid. Each half of the lambdoid suture bifurcates 

 at the mastoid portion of the temporal bone, the two divisions constituting the parieto-mastoid 

 and occipito-mastoid sutures; the point of bifurcation is known as the asterion. 



In the lower part of the view is seen the external occipital protuberance (iuion), the occipital 

 crest, and the three pairs of nuchal lines, which give it a rough and uneven appearance. The 

 occipital point is the point of the occiput furthest from the glabella in the median plane. It 

 is situated above the external occipital protuberance. 



(3) The Lateral Region 



The lateral region (norma lateralis) (fig. 127) is somewhat triangular in shape, 

 being bounded above by a line extending from the zygomatic process of the 

 frontal, along the temporal line to the lateral extremity of the superior nuchal line 

 of the occipital bone; this forms the base of the triangle. The two sides are 

 represented by hnes drawn from the extremities of the base to the angle of the 

 jaw. It is divisible into two portions, one in front, the other behind, the emi- 

 nentia articularis [tuberculum articulare]. The posterior portion presents, in a 

 horizontal line from behind forward, the mastoid portion of the temporal, with 

 its process and foramen, the external auditory meatus, the centre of which is 

 known as the auricular point, the mandibular fossa, and the condyle of the mandible 



In the anterior portion are three fossa), (a) temporal, (b) infratemporal, (c) 

 pterygo-palatine (spheno-maxillary), and two fissures, the inferior orbital (spheno- 

 maxillary) and pterygo-palatine. 



(a) The temporal fossa, somewhat semilunar in shape, is bounded above and behind by the 

 temporal line, in front by the frontal, zygomatic, and great wing of sphenoid, and laterally by 

 the zygomatic arch, by which it is separated superficially from the infratemporal fossa; more 

 deeply the infratemporal ridge separates the two fossae. 



The fossa is formed by parts of five bones, the zygomatic, temporal, parietal, frontal, 

 great wing of sphenoid, and is traversed bv six sutures, coronal, spheno-zygomatic, spheno- 

 squamosal, spheno-parietal, squamosal, and spheno-frontal. The point where the temporal 

 ridge is crossed by the coronal suture is the stephanion, and the region where the frontal, 

 sphenoid, temporal, and parietal meet is the pterion. The latter is frequently occupied in the 

 adult by the epipteric bone. 



The temporal fossa is concave in front, convex behind, filled by the temporal muscle, and 

 roofed in by a strong glistening aponeurosis, the temporal fascia, which serves to bind down 

 the muscle. 



(b) The infratemporal fossa (zygomatic fossa), irregular in shape, is situated below and 

 to the medial side of the zygoma, covered in part by the ramus of the mandible. It is bounded 

 in front by the lower part of the medial surface of the zygomatic, and by the infratemporal 

 surface of the maxilla, on which are seen the orifices of the posterior superior alveolar canals; 

 behind by the posterior border of the lateral pterygoid plate, the spine of the sphenoid, and the 

 articular tubercle; above by the infratemporal ridge, a small part of the squamous portion of 



