NORMA BASALIS OF THE SKULL. 157 
—the choane or posterior nares. Laterally the under surfaces of the great 
sphenoidal wings extend as far forward as the posterior border of the spheno- 
maxillary fissure ; whilst posteriorly they reach as far as the alar spine, external to 
which the spheno-squamosal suture, separating the great wing of the sphenoid from 
the squamous portion of the temporal, curves forwards and upwards, internal to the 
eminentia articularis, to reach the floor of the temporal fossa, along which its course 
has been already traced (p. 150). On a level with the front of the foramen 
magnum the jugular process of the occipital bone forms an irregular curved border, 
which sweeps outwards to terminate at a point just internal 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 internal 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 tabular portion of 
the occipital bone, an area which is limited behind by the superior curved 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 together with the petro-mastoid 
part of the same bone, the latter of which is wedged in between the great wing of 
the sphenoid in front and the occipital bone behind. Stretching forwards from the 
squamous temporal in front is seen the zygomatic process which, by its union with 
the malar, completes the formation of the zygomatic arch. 
Studying next the various parts in detail, the hard palate (palatum durum) may 
be first examined. Of horse-shoe shape as a rule, it presents many varieties of out- 
line and size. Formed by the palatal processes (processus palatini) of the superior 
maxill in front and the horizontal plates (partes horizontales) of the palate bones 
behind, its circumference in front and at the sides corresponds to the superior 
alveolar arch, in which are embedded the sixteen teeth of the upper jaw; 
posteriorly the edge of the hard palate is thin, ending mesially in a pointed 
process, the posterior nasal spine (spina nasalis posterior), on either side of which the 
posterior free border is sharp and lunated. The vault of the palate, which is 
concave from side to side, and from before backwards, varies in depth according to 
the projection and development of the alveolar processes. When the teeth are shed 
and the alveoli are absorbed, the palate becomes shallow and flat. Running 
throughout its entire length in the middle line is the middle palatine suture 
(sutura palatina mediana), which separates the palatal processes of the superior 
maxille in front and the horizontal plates of the palate bones behind. A little 
behind the central incisor teeth, and in the line of this suture, is a little pit, the 
anterior palatine canal or fossa (foramen incisivum). At the bottom of this may be 
seen the openings of some small canals, varying in number from one to four; these 
are usually described as arranged in two pairs, the one pair placed side by side, 
the other lying mesially in front and behind. The former are called the incisor 
foramina, or foramina of Stenson, and transmit the terminal twigs of the superior 
or descending palatine arteries which ascend to reach the nasal fossee. The latter, 
called the foramina of Scarpa, open, the anterior into the left, the posterior into the 
right nasal fossa, and afford passage for the fine filaments of the left and right naso- 
palatine nerves respectively. About half an inch (L2 mm.) in front of the posterior 
nasal spine the middle palatine suture is crossed at right angles by the transverse 
palatine suture (sutura palatina transversa). This, which indicates the line of 
- union of the palatal processes of the superior maxillee with the horizontal plates ot 
the palate bones, passes transversely outwards on either side until it reaches the 
inner aspect of the base of the alveolar process, along which it turns backward, to 
disappear within the posterior palatine canal (foramen palatinum majus), a hole 
which lies immediately internal to the root of the wisdom molar. Through this 
there pass the superior or descending palatine artery and the large descending 
_ palatine nerve. Leading from this foramen is a groove which curves forward im- 
- mediately to the inner side of the alveolar arch; not unfrequently the inner edge 
of this groove forms a thin and sharp ridge on the surface of the palate. In this 
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