SPHENOID BONE. 43 



anterior surface which assists in forming the outer wall of the orbit, 

 and an external surface, divided into two parts by the pterygoid 

 ridge. The superior part of the external surface enters into the 

 formation of the temporal fossa, and the inferior portion forms part 

 of the zygomatic fossa. The pterygoid ridge, dividing the two, 

 gives attachment to the upper origin of the pterygoideus externus 

 muscle. 



The spinous processes project backwards at each side from the 

 base of the greater wings of the sphenoid, and are received into the 

 angular intervals between the squamous and petrous portions of the 

 temporal bones. Piercing the base of each process is a large oval 

 opening, the foramen ovale ; nearer its apex a smaller opening, the 

 foramen spinosum ; and extending downwards from the apex a short 

 spine, which gives attachment to the internal lateral ligament of the 

 lower jaw and to the laxator tympani muscle. The external border 

 of the spinous process is rough, to articulate with the lower border 

 of the squamous portion of the temporal bone ; the internal forms 

 the anterior boundary of the foramen lacerum basis cranii, and is 

 somewhat grooved for the reception of the Eustachian tube. 



The pterygoid processes descend perpendicularly from the base of 

 the greater wings, and form in the articulated skull the lateral boun- 

 daries of the posterior nares. Each process consists of an external 

 and internal plate, and an anterior surface. The external plate is 

 broad and thin, giving attachment, by its external surface, to the 

 external pterygoid muscle, and by its internal surface to the internal 

 pterygoid. This plate is sometimes pierced by a foramen, which is 

 frequently formed by a process of communication passing between 

 it and the spinous process. The internal pterygoid plate is long 

 and narrow, and terminated at its extremity by a curved hook, the 

 hamular process, around which plays the tendon of the tensor palati 

 muscle. At the base of the internal pterygoid plate is a small 

 oblong depression, the scaphoid fossa, from which arises the cir- 

 cumflexus, or tensor palati muscle. The interval between the 

 two pterygoid plates is the pterygoid fossa ; andfthe two plates are 

 separated inferiorly by an angular notch (palatine), which receives 

 the tuberosity, or pterygoid process, of the palate bone. The ante- 

 rior surface of the pterygoid process is broad near its base, and 

 supports Meckel's ganglion. The base of the process is pierced by 

 the Vidian canal. 



Developement. By twelve centres ; four for the body, viz, two for 

 its anterior, and two for its posterior part ; four for the wings ; two 

 for the external pterygoid plates, and two for the sphenoidal spongy 

 bones. 



Articulations. With twelve bones ; all the bones of the head and 

 five of the face, viz. the two malar, two palate, and the vomer. 



Attachment of Muscles. To twelve pairs; temporal, external ptery- 

 goid, internal pterygoid, superior constrictor, tensor palati, laxator 

 tympani, levator palpebrse, obliquus superior, superior rectus, internal 

 rectus, inferior rectus, and external rectus. 



