BASE OF THE SKULL. 175 



the hard palate the pyramidal process of the palate bone appears wedged in 

 between the two plates, and so enters into the formation of the floor of the 

 pterygoid fossa. The medial pterygoid lamina separates the nasal cavity from the 

 pterygoid fossa; to the posterior edge of the medial pterygoid lamina are attached the 

 pharyngeal aponeurosis, the superior constrictor of the pharynx, and the pharyngo- 

 palatinus muscle. Above, the posterior border of this plate is channelled to form 

 the small scaphoid fossa, which curves laterally over the summit of the pterygoid 

 fossa, and furnishes a surface for the origin of the tensor veli palatini muscle. The 

 sharp medial margin of this fossa, continuous below with the posterior border of 

 the medial pterygoid lamina, extends upwards, and on either side of the body of 

 the sphenoid forms a blunt pointed process, the pterygoid tubercle, which extends 

 backwards towards the apex of the petrous part of the temporal bone. Just 

 lateral to this, and concealed by it, is the posterior extremity of the pterygoid 

 canal, through which pass the artery and nerve of the canal. The medial surface 

 of the medial pterygoid lamina is directed towards the nasal cavity. Superiorly 

 this surface curves medially to meet the inferior surface of the body of the sphenoid, 

 forming on either side a lipped edge, the vaginal process, between which the alse 

 of the vomer, which here forms the nasal septum, are wedged. Between the two 

 a small interval, however, is occasionally left, which forms on either side the basi- 

 pharyngeal canal. A little lateral to the line of union of the vaginal process with 

 the vomer is the opening of the pharyngeal canal. This lies between the inferior 

 surface of the vaginal process and the sphenoidal process of the palate bone, which 

 here articulates with the inferior surface of the body of the sphenoid. The 

 pharyngeal branch of the spheno-palatine ganglion and the pharyngeal branch of 

 the internal maxillary artery pass through this canal. Inferiorly the pterygoid 

 processes project below the level of the hard palate. The medial plate ends in a 

 slender recurved process, called the hamulus pterygoideus, which turns backwards 

 and laterally (this is frequently broken off in skulls which have been roughly 

 handled). It reaches as low as the level of the alveolar margin, and lies just 

 within and behind the posterior extremity of the alveolar process. It can readily 

 be felt in the living by placing the finger against the soft palate behind and just 

 within the gum around the root of the dens serotinus (O.T. wisdom tooth). On 

 the front of and below this process the tendon of the tensor veli palatini muscle 

 glides in a groove. 



. The choanae (O.T. posterior nares) lie between the two pterygoid processes. 

 Of a shape much resembling two Gothic windows, their bases or inferior boundaries 

 are formed by the horizontal part of the palate bone. Laterally they are bounded 

 by the medial surfaces of the medial pterygoid laminae, whilst above, the lateral 

 side of the arch is formed by the vaginal processes of the same laminae ; medially 

 they are separated by the thin vertical posterior border of the vomer, whilst, 

 above, the everted alae of the same bone form the medial sides of the arch. The 

 plane of these apertures is not vertical but oblique, corresponding usually to a line 

 drawn from the bregma above through the last molar tooth of the maxilla below. 

 Their size varies considerably, but the height is usually equal to twice the width. 



The region of the cranium which lies lateral to the maxilla and lateral 

 pterygoid lamina corresponds to the infra-temporal fossa, which has been already 

 described, as it is seen from the side (Lateral Aspect of the Skull, p. 168). Viewed 

 from below, the infra-temporal fossa is bounded in front by the infra-temporal 

 surface of the body of the maxilla and the medial surface of the zygomatic bone. 

 The roof, which is traversed by the spheno-squamosal suture, is formed in front by 

 the inferior surface of the great wing of the sphenoid, and behind by a small 

 triangular surface of the under side of the squamous part of the temporal bone, 

 immediately in front of the tuberculum articulare. 



Circumscribed laterally and behind by the anterior root of the zygoma, which 

 curves forward to become continuous in front with the infra-temporal crest crossing 

 the lateral surface of the great wing of the sphenoid, the roof of the fossa is 

 separated from its anterior wall by the inferior orbital fissure, which is so inclined 

 that with its fellow of the opposite side it forms an angle of 90. Superiorly the 

 infra-temporal fossa communicates freely with the temporal fossa medial to the 



