236 Anatomy of Skeleton 



introduced really to explain not only the occurrence of double fissures, but also the presence of 

 teeth bearing unusual relation to clefts in the palate and alveolus. These extra teeth, however, 

 are more rationally explained on the assumption of breaking up of the dental epithelial area over 

 the situation of the cleft. 



The palate is considerably narrower in female skulls than in those of the other sex. 



Spheno-maxillary Fossa. 



The student should now examine the spheno-maxillary fossa with great care, 

 so that he may gain a clear comprehension of the way in which it is built up and of 

 its relations and connections, for the key to an understanding of a great deal of the 

 deep anatomy of the face is to be found in this region. 



We have seen that the palate bone is applied to the inner side of the maxilla, 

 but that it projects back further than this bone to articulate with the internal ptery- 

 goid plate, so holding the jaw away from the pterygoid region by the amount of this 

 projection, and thus leading to the existence of an interval between them that is the 

 spheno-maxillary fossa. Evidently the vertical plate of the palate must form the inner 

 wall of this fossa and must separate it from the nose, for this plate is part of the outer 

 wall of the nasal fossa. Because the vertical plate articulates behind with the internal 

 pterygoid plate along the whole length of its front border it is equally plain that the 

 posterior wall of the fossa must be formed by the outer plate (Fig. 183) except in its 

 extreme upper and inner part, where trie inner plate is slightly wider than its front 

 edge that carries the palate bone : in other words, the front edge of the internal plate 

 turns in under the body of the sphenoid and thus leaves a small piece of the plate 

 exposed to form part of the back wall of the fossa just-below and outside the body of 

 the bone. This is the level of the Vidian opening, which is seen immediately outside 

 this little piece of inner plate. Outside this the external pterygoid plate makes the 

 chief part of the posterior wall : the plate broadens rapidly as it passes up and becomes 

 continuous with the area of bone immediately below the orbital surface of the great 

 wing. 



In Fig. 183 the back wall of the fossa is shown, and the outer plate is seen to widen 

 very much in its upper part and to open out into the spheno-maxillary surface of the 

 great wing. The position of the vertical plate of the palate is also shown, and the small 

 part of the inner plate that enters into the formation of the back wall. At the outer 

 edge of the broad front surface of the outer plate the fossa becomes continuous with 

 the zygomatic fossa, so it is evident that the breadth of the fossa depends on the width 

 of the surface of the plate ; this varies in different bones, leading to a shallow or deep 

 fossa, as the case may be. The opening, bounded by a margin of the plate, through 

 which the fossa becomes continuous with the zygomatic fossa may be termed the ptery go- 

 maxillary fissure, to distinguish it from the spheno-maxillary fissure, which opens into the 

 orbit from the fossa. Observe that the anterior opening of the foramen rotundum 

 is on the spheno-maxillary surface of the great wing, so that the nerve enters the fossa 

 on leaving the foramen ; also notice that the Vidian opening is further in, and on a 

 lower level, because it runs between the two plates and not through the great wing. 

 A ridge of bone separates the two foramina and can be traced up to the side of the body 

 of the bone. The inner wall of the fossa is made by the vertical plate of the palate. 

 Articulate this bone with the maxilla and observe how the front portion of the vertical 

 plate lies against the nasal surface of the maxilla, so that its orbital process can be 

 seen from behind the jaw, at the top back corner of the bone, as it turns out to reach 

 the orbit ; in this way the orbital process comes to possess a zygomatic surface. The 

 spheno-palatine foramen separates this process from the sphenoidal process, which is 

 directed in as it follows the internal plate under the body of the sphenoid. 



