LATERAL ASPECT OF THE SKULL. 169 



through which a vein runs from the cavernous sinus within the cranium to the 

 pterygoid venous plexus situated in the infra -temporal fossa. 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 angular 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 to and from the cranium, viz., the 

 mandibular division of the trigeminal nerve, together with its motor root, and the 

 accessory meningeal artery through the foramen ovale, and the middle meningeal 

 artery and its companion vein through the foramen spinosum. A part of the 

 squamous part of the temporal also forms a small portion of the roof of this fossa ; it 

 consists of a triangular area immediately in front of the tuberculum articulare, and 

 between it and the anterior root of the zygomatic process of the temporal, which is 

 here curving medially and forwards, to become continuous with the infra-temporal 

 crest. Medially this surface is continuous with the infra- temporal surface of the 

 great wing of the sphenoid, separated from it, however, by the posterior part of the 

 spheno-squamosal suture. 



When the mandible is in position, the infra-temporal fossa is concealed by the 

 ramus of the mandible, the medial surface of which, in its upper half, forms the 

 lateral wall of that space. Viewed from the lateral side, the ramus of the mandible 

 displays considerable differences in different skulls. These are mainly due to varia- 

 tions in its width and in the nature of the angle which it forms at its fusion with 

 the body of the bone. A considerable interval separates the posterior border of the 

 ramus from the front of the mastoid process. Within this space may be seen the 

 free inferior edge of the tympanic plate (vaginal process), from which, just below 

 the external acoustic meatus, the styloid process of the temporal bone is observed 

 passing downwards and slightly forwards. The width and height of the coronoid 

 process vary much, oftentimes reaching the level of the top of the condyle. Its 

 extremity, when the lower jaw is closed, lies just within the anterior part of the zygo- 

 matic arch ; at other times it rises to a much higher level, so that its point may be 

 seen above the level of the upper border of the zygomatic arch. The posterior 

 edge of the coronoid process forms the anterior border of the mandibular notch, 

 and limits in front the interval left between the lower border of the posterior half 

 of the zygomatic arch and the upper hollowed edge of the ramus. On looking into 

 this interval, the floor of the infra-temporal fossa may be seen, formed anteriorly by 

 the lateral pterygoid lamina ; whilst posteriorly it is possible to pass a probe right 

 across the base of the skull from one mandibular notch to the other, the shaft of 

 the probe lying immediately behind the pterygoid processes of the sphenoid, and 

 crossing the foramina ovalia, through which the mandibular divisions of the tri- 

 geminal nerves pass. 



The ramus and coronoid process are so placed as to occupy a position inter- 

 mediate between the zygomatic arch laterally and the lateral pterygoid lamina 

 medially; their medial surface, therefore, forms the lateral wall of the infra-temporal 

 fossa. On a level with the surface of the crowns of the teeth of the mandible, 

 and situated about the middle of this aspect of the ramus, is the mandibular 

 foramen, the superior opening of the canalis mandibulas (mandibular canal), which 

 traverses the body of the bone. Through this foramen there pass the inferior 

 alveolar branch of the mandibular division of the trigeminal nerve, together 

 with the inferior alveolar artery and its veins. As will now be seen, when the 

 mandible is in position, the infra -temporal fossa is closed in laterally by the 

 ramus of the mandible. In front there is an interval between the anterior border 

 of the ramus and the infra-temporal surface of the maxilla, through which pass 

 the buccinator branch of the trigeminal nerve and the communicating vein 

 between the pterygoid plexus and the anterior facial vein. Above, in the 

 interval between the mandibular notch and the inferior border of the zygomatic 

 arch, there pass from the fossa the vessels and nerves which supply the masseter 

 muscle. Between the posterior border of the ramus and the styloid process there 

 enter and leave the large vessels which are found within the space. Superiorly 

 under cover of the zygomatic arch, the infra-temporal fossa communicates with the 



