38 SPHENOID BONE. 



surface is continuous on each side with the spinous process, and at the 

 angle of union is the termination of the Vidian canal. 



The lesser wings (processes of Ingrassias) are thin and triangular, 

 the base being attached to the upper and anterior part of the body of 

 the sphenoid, and the apex extended outwards, and terminating in an 

 acute point. The anterior border is irregularly serrated, the posterior 

 being free and rounded and received into the fissure of Sylvius of the 

 cerebrum. The inner extremity of this border is the anterior clinoid 

 process, which is supported by a short pillar of bone, giving attach- 

 ment to a part of the common tendon of the muscles of the orbit. 

 The lesser wing forms the posterior part of the roof of the orbit, and its 

 base is traversed by the optic foramen. 



The greater wings present three surfaces; a superior or cerebral, 

 which forms part of the middle fossa of the base of the skull, an ante- 

 rior 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 angu- 

 lar intervals between the squamous and petrous portions of the tem- 

 poral 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 ante- 

 rior 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 ex- 

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

 pterygoid. This plate is sometimes pierced by a foramen, which is not 

 unfrequently 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 hamu- 

 lar process, around which plays the tendon of the tensor palati muscle. 

 At the base of the internal pterygoid plate is a small oblong depres- 

 sion, the scaphoid fossa, from which arises the circumflexus or tensor 

 palati muscle. The interval between the two pterygoid plates is the 

 fttrygoid fossa ; and the two plates are separated inferiorly by an an- 

 gular notch (palatine) which receives the tuberosity, or pterygoid 



