THE BONES OF THE HEAD 89 



The external pterygoid plate is broader and shorter than the 

 internal, and is directed backwards and shghtly outwards. Its 

 . outer surface looks into the zygomatic fossa, and gives origin to the 

 lower head of the external pterygoid muscle. Its inner surface looks 

 into the pterygoid fossa, and gives origin to the internal pterygoid 

 muscle. The posterior border usually presents towards its upper 

 part a sharp spine, from which the pterygo-spinous ligament extends 

 backwards and outwards to the spinous process. This ligament 

 sometimes becomes ossified, and a foramen is then formed, called the 

 pterygo-spinous foramen, for the passage of muscular branches of 

 the inferior maxillary nerve. 'Sometimes there is another spine 

 towards the lower end of this border for another pterygo-spinous 

 ligament. 



The internal pterygoid plate, narrower and longer than the 

 external, is prolonged inferiorly into the hamular process, which 

 is inclined outward , its outer and inferior aspects being smooth 

 and grooved for the play of the tendon of the tensor or circum- 

 flexus palati. Superiorly this plate is inflected as the vaginal 

 process, which articulates with the ala of the vomer, and presents 

 on its under surface a groove forming part of the pterygo-palatine 

 canal already referred to. The outer surface of the internal 

 pterygoid plate looks into the pterygoid fossa, and is related to 

 the tensor or circumflexus palati. The inner surface forms the 

 back part of the outer wall of the nasal fossa. The posterior 

 border at its upper end presents the pterygoid tubercle, which 

 has the posterior end of the Vidian canal above and external to it. 

 Between this tubercle and the Vidian canal on the one hand, and 

 the pterygoid fossa on the other, is the scaphoid fossa, which 

 gives origin to the tensor or circumflexus palati. On the posterior 

 border of the internal pterygoid plate, below the lower pointed 

 end of the scaphoid fossa, is the Eustachian spine or processus 

 tubarius, which supports the cartilage of the Eustachian tube. 

 The lower third of the posterior border aad the hamular process 

 give origin to fibres of the superior constrictor muscle of the 

 pharynx, and the hamular process also gives attachment to the 

 pterygo-mandibular ligament. The anterior border articulates with 

 the posterior border of the perpendicular plate of the palate bone. 



The Vidian or pterygoid canal pierces the bone from before back- 

 wards at the junction of the internal pterygoid plate and body on 

 either side. Its anterior orifice appears on the posterior wall of the 

 spheno-maxillary fossa, below and internal to the anterior orifice 

 of the foramen rotundum, and posteriorly it opens on the anterior 

 wall of the foramen lacerum medium, above and external to the 

 pterygoid tubercle. It gives passage to the Vidian nerve and artery. 

 Summary of Openings in the Sphenoid Bone. — (i) Sphenoidal 

 fissure, between small and great wings ; (2) optic foramen, between 

 the two roots of the small wing ; and, in the great wing, (3) foramen 

 rotundum ; (4) foramen ovale ; (5) foramen Vesalii (inconstant) ; 

 (6) foramen spinosum ; (7) canaliculus innominatus (inconstant) ; 



