198 Anatomy of Skeleton 



pterygoid plate, so that the upper jaw is held away from the pterygoid plate by this 

 projection of the palate. Look at the skull from the side and see that the external 

 pterygoid palate is separated by an interval (spheno-maxillary fossa) from the maxilla, 

 and this fossa has its inner wall made by the vertical plate of palate passing back from 

 the inner aspect of the maxilla to articulate with the internal pterygoid plate : thus the 

 vertical plate separates the spheno-maxillary fossa from the nasal cavity. 



The fossa is closed below by a mass of bone, which, in the complete skull, appears 

 to be part of the maxilla, articulating with the lower parts of the pterygoid plates ; 

 but this is not really so, for the maxilla does not come at all into contact with the plates, 

 but is separated from them by this bone, which is the tuberosity of the palate pro- 

 truding downwards and outwards behind the maxilla and thus firmly welding it to 

 the pterygoid plates (see Fig. 161). So it is evident that the bones of the face are not 

 only attached above to the cranial bones, but are also buttressed behind by the ptery- 

 goid plates, and, through the zygoma, by the temporal. 



For a complete list of the names applied to different points on the skull as used in 

 craniometry the reader must consult works dealing with that subject, but as some of 

 these terms are in common use in description it is convenient to give a list of these here, 

 with an indication of their meaning. 



In the middle line : 



Nasion. Junction of nasal and frontal bones. 

 Glabella. Mid-point at level of superciliary ridges. 

 Bregma. Junction of coronal and sagittal sutures. 

 Lambda. Junction of sagittal and lambdoid sutures. 

 Inion. External occipital protuberance. 



At the side of the skull : 



Auricular Point. Centre of external meatus. 



Asterion. Region where occipital, parietal, and temporal meet. 



Pierian. Region where frontal, parietal, sphenoid, and temporal meet. 



Reid's base-line is used for certain surgical surface markings : it is drawn 

 back (Fig. 168) from the lower margin of the orbital opening through the auricular 

 point, and when prolonged back passes a little distance below the inion. 



SEPARATE BONES OF THE SKULL. 



When examining the individual bones the student should have beside him a com- 

 plete or half-skull in addition to the disarticulated bones. Every point observed on 

 the separate bone ought to be verified and extended on the whole skull, and the general 

 position of the particular bone in the skull must be continuously borne in mind. In 

 this way the individual bone and its related structures are followed and comprehended 

 as parts of a connected whole, and the meaning of its attachments, etc . , becomes apparent, 

 while at the same time an extended knowledge of the whole skull is gradually built up 

 that enables one to understand it much more fully on going over it again. 



FRONTAL BONE. 



A tabular bone forming the front of the cranial region and a small portion of the 

 temporal fossa laterally, but also sending back from its lower border two orbital plates 

 which make the greater part of the roof of each bony orbit. 



