THE SPHENOID BONE. 137 



small vein. Occasionally there is a small foramen (canaliculus innominatus) 

 to the medial side of the, foramen spinosum for the transmission of the small 

 superficial petrosal nerve. 



The external surface of the great wing enters into the formation of the walls of 

 the orbital, temporal, infra-temporal, and pterygo-palatine fossae by three well- 

 defined areas ; of these the upper two, i.e. the orbital and the temporal, are separated 

 by an oblique jagged ridge, the margo zygomaticus (zygomatic border), for articula- 

 tion with the fronto-sphenoidal process of the zygomatic bone. Occasionally the 

 lower part of this ridge articulates with the zygomatic process of the maxilla. 

 The facies orbitalis (orbital surface) lies to the medial side of this crest and 

 is directed forwards and a little medially ; of quadrilateral shape, it forms the 

 posterior and lateral wall of the orbit ; plane and smooth, it is bounded posteriorly 

 by the sharp inferior free margin of the superior orbital fissure, towards the medial 

 extremity of which a pointed spine (spina recti lateralis), for the attachment 

 of the inferior common ligament of origin of the ocular muscles, can usually 

 be seen. It is limited superiorly by the edge of a rough triangular area which 

 articulates with the frontal bone ; anteriorly by the zygomatic border ; whilst 

 inferiorly a free, well-defined oblique margin constitutes the posterior and lateral 

 boundary of the fissura orbitalis inferior (inferior orbital fissure), which separates 

 this part of the bone from the orbital surface of the maxilla. Below this border 

 there is a grooved surface which leads medially toward the orifice of the foramen 

 rotundum. In the articulated skull this forms part of the posterior wall of the 

 pterygo-palatine fossa. 



To the lateral side of the zygomatic border, which bounds it in front, is the 

 facies temporalis (temporal area), concavo-convex from before backwards. It slopes 

 medially below, where it is separated from the spheno-maxillary area by a well- 

 marked muscular ridge, the crista infratemporalis (infra-temporal crest). Behind, the 

 temporal surface is bounded by the margin of the great wing which articulates 

 with the squamous part of the temporal (margo squamosus), and above by the edge 

 which unites it with the sphenoidal angle of the parietal and with the frontal bone. 

 The temporal surface enters into the formation of the floor of the fossa of the same 

 name, and affords an extensive attachment to the fibres of origin of the temporal 

 muscle. The facies sphenomaxillaris (spheno-maxillary surface), the third of the 

 areas above referred to, is situated below the infra-temporal crest, and corre- 

 sponds to the under surface of the posterior half of the great wing ; it extends 

 as far back as the angular spine and posterior border. Opening on it are seen 

 the orifices of the foramen spinosum and ovale. It is slightly concave from side 

 to side, and is confluent medially with the lateral surface of the lateral pterygoid 

 plate. In front, it is bounded by a ridge which curves upwards and laterally 

 from the anterior part of the lateral pterygoid plate to join the infra-temporal crest. 

 In the articulated skull this ridge forms the posterior boundary of the pterygo- 

 maxillary fissure. The spheno-maxillary surface overhangs the infra-temporal 

 fossa, and affords an origin for the superior head of the external pterygoid muscle. 



The processus pterygoidei (pterygoid processes) spring from the inferior surface 

 of each lateral aspect of the body as well as from the under side of the roots 

 of the great wings, and pass vertically downwards. Each consists of two laminae, 

 the lateral and medial laminae of the pterygoid process, fused together anteriorly, and 

 enclosing between them posteriorly the pterygoid fossa. 



The lateral pterygoid plate, thin and expanded, is directed obliquely back- 

 wards and laterally, its lower part being often somewhat everted. Its posterior 

 edge is sharp, and often has projecting from it one or two spines, to one of which 

 (processus pterygospinosus) the pterygo-spinous ligament, which stretches towards 

 the angular spine, is attached. Laterally it furnishes an origin for the inferior 

 head of the external pterygoid muscle, and on its medial side, where it forms the 

 lateral wall of the pterygoid fossa, it supplies an attachment for the internal 

 pterygoid muscle. 



The medial pterygoid plate is narrower and somewhat stouter. By its 

 medial aspect it forms the posterior part of the lateral wall of the nasal cavity ; 

 laterally it is directed towards the pterygoid fossa. Its posterior edge ends 



