152 OSTEOLOGY. 
tabular plate of the occipital, there is usually a foramen (mastoid) for the trans- 
mission of an emissary vein from the lateral sinus within the cranium to the 
cutaneous occipital vein of the scalp; this opening, which may be double, varies 
greatly in size, and is usually placed on a level with the external auditory 
meatus. 
Zygomatic Fossa.—The side of the cranium in front of the anterior root of the 
zygomatic process of the temporal bone is deeply hollowed, forming the zygomatic 
or infratemporal fossa (fossa infratemporalis); this in topographical anatomy 
corresponds to the pterygo-maxillary region. The student must bear in mind 
that, in examining this space, the ramus and coronoid process of the lower 
jaw form its outer wall; but this bone for the present being withdrawn, enables us 
to get a better view of the boundaries of the space. In front its anterior wall 
is formed by the convex posterior or zygomatic surface (facies infratemporalis) 
of the superior maxilla, which rises behind the socket for the last molar tooth to 
form the tuberosity (tuber-maxillare). Anteriorly the zygomatic surface of the 
upper jaw is separated from its facial aspect by the sharp inferior margin of the malar 
or zygomatic process which supports the malar bone. This latter curves outwards 
and backwards, forming part of the upper and anterior wall of the fossa. On the inner 
surface of this wall will be seen the suture uniting the malar and superior maxillary 
bones (sutura zygomatico-maxillaris), which runs obliquely upwards and inwards 
to reach the external extremity of the spheno-maxillary fissure, the lower border of 
which forms the superior boundary of the zygomatic surface of the upper jaw. On 
this aspect of the bone are to be seen the openings of the posterior dental canals 
(foramina alveolaria) two or more in number, which transmit the nerves and 
vessels to the upper molar teeth. The inner wall of the zygomatic fossa is formed 
by the outer surface of the external pterygoid plate (lamina lateralis processus 
pterygoidei), the width and shape of which varies greatly; its posterior border is 
thin and sharp, and often furnished with spiny points, to one of which the pterygo- 
spinous ligament, which stretches from this border to the alar spine of the sphenoid, 
is attached. It occasionally happens that this ligament becomes  ossified. 
Anteriorly the external pterygoid plate is separated from the superior maxilla 
above by an interval called the pterygo-maxillary fissure. Below this the bones are 
apparently fused, but a careful inspection of the skull, together with an examina- 
tion of the disarticulated bones, will enable the student to realise that, wedged in 
between the two bones at this point, is a part of one of the smaller bones of the 
face, the tuberosity of the palate bone (processus pyramidalis ossis palatini). 
The lower border of the external pterygoid plate is usually curved and slightly 
everted. Superiorly, where the external pterygoid plate is generally narrower, it 
sweeps upwards to become continuous with the broad under surface of the great 
wing of the sphenoid; this, which overhangs in part the zygomatic fossa superiorly, 
is limited above by the infratemporal crest which separates its zygomatic from its 
temporal surface. The zygomatic surface of the great wing of the sphenoid is 
limited in front and below by the edge which forms the upper boundary of the 
spheno-maxillary fissure, whilst behind it reaches as far back as the inner 
extremity of the Glaserian fissure, where it terminates in the alar spine. It is 
from this point that the suture (sutura spheno-squamosa) curves forward and 
upwards to reach the region of the pterion. The infratemporal or zygomatic 
surface of the great wing of the sphenoid, and the outer surface of the external 
pterygoid plate, alike afford extensive attachments for the external pterygoid 
muscle, whilst the former is pierced by minute canals for the transmission of 
emissary veins. Occasionally a larger vascular foramen is present (foramen Vesalit), 
through which a vein runs from the cavernous sinus within the cranium to the 
pterygoid venous plexus situated in the pterygo-maxillary region. Immediately 
behind the root of the external pterygoid plate there is a large oval hole, the foramen 
ovale, and behind that, and in line with the alar spine, is the smaller foramen 
spinosum. ‘These two foramina cannot usually be seen in a side view of the skull, 
and are better studied when the base is examined; they are mentioned, however, 
because they transmit structures which here pass from and enter the cranium, viz. 
the inferior maxillary division of the fifth nerve, together with its motor root, and 
