234 Anatomy of Skeleton 



(b) an ethmoidal (upper) surface, which supports the ethmoid and shows a 

 crest for the middle turbinal, a part of the ethmoid ; 



(c) a spheno-maxillary (or zygomatic) surface, looking outwards and backwards 

 behind the maxilla and therefore into the spheno-maxillary fossa ; ^fS* 



(d) an orbital (terminal) surface, visible between ethmoid and maxilla in the 

 floor of the 



The sphenoidal process has : 



(a) An outer or spheno-maxillary surface ; 



(b) an inner or nasal surface ; 



(c) an upper terminal part applied to the sphenoidal body. 

 It is grooved behind by the margin of the internal pterygoid plate. 



The vertical plate below the processes and notch has an inner surface that is purely 

 nasal, crossed by a rough ridge that carries the lower turbinate bone, and an outer surface 

 that is mostly maxillary, but has a small triangular area behind this and immediately 

 below the notch (Fig. 187) which forms the inner wall of the spheno-maxillary fossa. 

 Below this the tuberosity begins to grow out from the bone. On this surface of the plate, 

 in front of the tuberosity, the posterior palatine groove is seen running downwards and 

 forwards : this part of the bone is applied to the maxilla, which therefore completes 

 the canal. The lower part of the groove may be partly or completely closed in by the 

 tuberosity. 



The horizontal plate has rough articular front and inner margins for the maxillary 

 palate and its fellow respectively, a concave posterior edge to which the palatine apo- 

 neurosis (soft palate) is attached, with a prominent posterior nasal spine centrally, 

 where the Azygos uvulae muscle arises, a rough lower surface, and a smooth upper or 

 nasal surface which forms a prominent median crest with its opposite fellow, for the 

 support of the vomer. 



The tuberosity extends in a direction downwards and outwards and slightly back- 

 wards. It has a rough antero-external maxillary surface, separated by the posterior 

 palatine groove from the maxillary surface of the vertical plate, and a posterior surface 

 which is applied to the front of the pterygoid processes. This surface (Fig. 187) shows 

 a deep groove internally for the internal pterygoid plate, a rough articular area obliquely 

 directed by its outer margin for the outer plate, and a shallow concave fossa between 

 these that completes the floor of the pterygoid fossa (see Fig. 161) and gives origin to 

 fibres of the Internal Pterygoid muscle. This origin extends on to the lower surface 

 (Fig. 161) of the tuberosity and from this runs on to the outer part, which is visible 

 between the external plate and maxilla. 



This origin of part of Internal Pterygoid gives its front and lower fibres the appearance of being 

 superficial to the lower fibres of the External Pterygoid. 



Articulations. With the maxilla (vertical plate, horizontal plate and tuberosity), 

 ethmoid and inferior turbinal (vertical plate), sphenoid (vertical plate and tuberosity), 

 vomer and its fellow (horizontal plate). 



Development. 



The bone is developed in membrane on the inner aspect of the cartilaginous nasal 

 capsule, from a centre that appears during the eighth week in the region of the future 

 tuberosity ; from this ossification extends into the palate fold as this meets its fellow, 



