NORMA VERTICALIS OF THE SKULL. 155 
the digastric muscles, thus causing these processes to appear more pointed when 
viewed from this aspect. 
NorRMA VERTICALIS. 
This is the view of the calvaria as seen from above. It is liable to great 
diversities of form. Thus its shape may vary from an elongated oval to an outline 
more nearly circular. These differences have been classified, and form important 
distinctions from a craniometrical standpoint (p. 173), the rounder varieties being 
termed the brachycephalic, whilst the elongated belong to the dolichocephalic croup. 
Another noteworthy point in this view is the fact that in some instances the 
zygomatic arches are seen, whilst in others they are concealed by the overhang 
and bulge of the sides of the fore part of the cranium. The former condition is 
described as phenozygous, the latter as cryptozygous, and each is more or less closely 
associated with the long or round varieties of head-form respectively. 
The sutures displayed have a T-shaped arrangement. Placed mesially between 
the two parietal bones is the sagittal suture. This is finely denticulated, except in 
the region of the obelion, though, of course, this will not be apparent if obliteration 
of the suture has taken place through fusion of the two parietal bones. Posteriorly 
the sagittal suture unites with the lambdoid suture at the lambda, which marks in 
the adult the position of the posterior fontanelle of the fcetus. Anteriorly it 
terminates by joining the transverse suture which separates the frontal bone 
anteriorly from the parietals behind ; this latter is called the coronal suture, and the 
point of junction between the sagittal and coronal suture is known as the bregma, 
which 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 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 occasionally be seen the 
post-coronal depression (p. 150), 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. 
NorMA BASALIS. 
The base of the cranium—.e. the skull without the mandible—includes a descrip- 
tion 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 
superior maxillee and palate bones, the superior dental arch, and the bodies of the 
superior maxille as seen from below ; whilst externally, and united with the bodies of 
the superior maxilla, the malar bones are displayed, curving backwards to form the 
anterior halves of the zygomatic arches. In the middle line, 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 magnum for the 
transmission of the spinal cord and its membranes. In front of this a stout bar of 
bone extends forwards in the middle line, formed by the union of the body of the 
‘sphenoid in front with the basilar process of the occipital bone behind. In adult 
skulls all trace of the fusion of these two bones has disappeared ; when union is in- 
complete, it indicates that the skull is that of a person below the age of twenty-five. 
