46 



THE BONES -OF THE HEAT). 



great wing is concave, and forms part of the middle fossa of the naseof the cranium. 

 The external surface (temporo-zygomatic) is divided by a ridge, infratemporal crest, 

 into an inferior part, which looks downwards into the zygomatic fossa, and an elongated 

 superior part, looking outwards, which forms a part of the temporal fossa (fig. 68, 

 p. 66). The anterior surface looks forwards and inwards, and consists of a quadri- 

 lateral orbital portion, which forms the back part of the external wall of the orbit, and 

 of a smaller inferior portion which overhangs the pterygoid process, looks into the 

 spheno-maxillary fossa, and is perforated by the foramen rotundum. The posterior 

 border in its mesial part bounds the foramen lacerum, in its lateral part articulates 



GREAT WING 



SMALL WING 

 BODY 



SPHEN. FISS. 



ETHM. SPINE OPT. FOR. / ORB. SURF 



SPH.FOH 



FRATEMP. 

 CREST 



ZYCOM. SURF. 



SPHENO-MAX. SURF. 

 EXT. PTERYC. PLATE 



PTERYC. NOTCH 



IAMULAR PROC. 



PTERYCOID PROCESS 



Fig. 46. THE SPHENOID BONE, FROM BEFORE. (Drawn by D. Gnnn. ) 



with the petrous, and forms with that a groove on the under aspect for the carti- 

 laginous part of the Eustachian tube.. The external margin articulates with the 

 squamous, and the extremity overlaps the anterior inferior angle of the parietal. In 

 front of this comes a triangular surface, the sides of which are formed by the upper 

 margins of the cerebral, orbital, and temporal surfaces respectively, for articulation 

 with the frontal bone. The anterior margin, between the orbital and temporal 

 surfaces, articulates with the malar bone ; and below this is a short horizontal free 

 elge separating the zygomatic and spheno-maxillary surfaces. Above and internally 

 the orbital and cerebral surfaces meet at the sharp border which forms the inferior 

 boundary of the sphenoiual fissure, and which is frequently marked at its inner part 

 by a small projection giving attachment to the lower head of the external rectus 

 muscle of the eyeball. 



The pterygoid processes project downwards and slightly forwards from the 

 adjacent parts of the body and the great wings. Each consists of two plates united 

 in front and diverging behind, so as to enclose between them the pterygoid fossa, in 

 which the internal pterygoid muscle arises. The external pterygoid plate, broader 

 than the internal, lies in a plane extending backwards and outwards ; its outer 

 surface bounds the zygomatic fossa, and is impressed by the external pterygoid 



