172 OSTEOLOGY. 



anteriorly from the parietals posteriorly; this latter is called the coronal suture, and the 

 point of junction between the sagittal and coronal sutures is known as the bregma ; 

 this corresponds in position to the anterior fontanelle of the foetus. The summit 

 of the vault of the calvaria corresponds to a variable point in the line of the sagittal 

 suture, and is named the vertex. The coronal suture is less denticulated centrally than 

 laterally. Occasionally there is a persistence of the suture (metopic) which unites 

 the two halves of the frontal bone ; under these conditions the line of the sagittal 

 suture is carried forward to the fronto-nasal suture, and a skull displaying this 

 peculiarity is described as metopic. Behind the coronal suture may occasion- 

 ally be seen the post-coronal depression, and in some instances the vault of the 

 calvaria forms a broad, slightly elevated crest along the line of the sagittal suture. 

 On either side the temporal ridges can be seen curving over the lateral and superior 

 aspects of the parietal bones. As the lower of these crosses the coronal suture in 

 front it marks a spot known as the stephanion, useful as affording a fixed point 

 from which to estimate the bi-stephanic diameter. The interval between the 

 temporal ridges on either side will vary according to the form of the skull and the 

 development of the temporal muscle. In this view of the calvaria a small part of 

 the lambdoid suture on either side of the lambda is visible posteriorly. 



Basis Cranii Externa (Norma Basalis). 



The external or inferior aspect of the base of the cranium i.e. the skull without 

 the mandible includes a description of the under surfaces of the skeleton of the 

 face (cranium viscerale) and the cranium (cranium cerebrale). The former includes 

 the hard palate formed by the maxillse and palate bones, the superior alveolar arch, 

 and the bodies of the maxillse as seen from below ; whilst laterally, and united with 

 the bodies of the maxillse, the zygomatic bones are displayed, curving backwards 

 to form the anterior halves of the zygomatic arches. In the median plane, passing 

 from the upper surface of the hard palate, is the osseous septum of the nose, 

 here formed by the vomer, which is united above to the under surface of the body 

 of the sphenoid. 



The under surface of the cranium is pierced by the foramen occipitale magnum 

 for the transmission of the spinal medulla and its membranes. In front of this a 

 stout bar of bone extends forwards in the median plane, formed by the union of the 

 body of the sphenoid in front with the basilar part of the occipital bone behind. 

 In adult skulls all trace of the fusion of these two bones has disappeared ; when 

 union is incomplete, it indicates that the skull is that of a person below the age of 

 twenty-five. The sphenoid comprises that part of the calvaria which forms the roof 

 and sides of the apertures which lie on either side of the nasal septum above the 

 hard palate the choanae. Laterally the inferior surfaces of the great wings of the 

 sphenoid extend as far forward as the posterior border of the inferior orbital fissure ; 

 whilst posteriorly they reach as far as the angular spine, lateral to which the 

 spheno-squamosal suture, separating the great wing of the sphenoid from the 

 squamous portion of the temporal, curves forwards and upwards, medial to the 

 tuberculum articulare, to reach the floor of the temporal fossa, along which its course 

 has been already traced (p. 168). On a level with the front of the foramen 

 magnum the jugular process of the occipital bone forms an irregular curved border, 

 which sweeps laterally to terminate at a point just medial to the root of the 

 styloid process. Here, in line with the spheno-squamosal suture, from which, how- 

 ever, it is separated by a considerable interval, its extremity turns backwards, and 

 may be traced at first medial to, and then turning upwards, behind the mastoid 

 process of the temporal bone, separated from this latter by the occipito-mastoid 

 suture. The bone behind the foramen magnum, which is included between the 

 two occipito-mastoid sutures, comprises the nuchal surface of the squamous portion 

 of the occipital bone, an area which is limited behind by the superior nuchal line, 

 which separates it from the occipital surface of the same bone. The remaining 

 portions of the base of the calvaria, as at present exposed, are formed by the 

 squamous and tympanic portions of the temporal bone, together with the petro-mastoid 

 part of the same bone, the latter of which is wedged in between the great wing of 



