THE SPHENOID BONE. 



189 



Fig. 211 



Carotico 

 clinoid 

 foramen 

 lies be- 

 neath 

 spur of 

 bone 



Anterior 



Middle 



Posterior 



clinoid 



processes 



Sphenoid bone, showing abnormal development of 

 middle clinoid processes, especially on the left side. Re- 

 duced one-half. 



enclose a canal, commonly called the optic for a77ien,^ for the optic nerve, which is 

 accompanied by the ophthalmic artery. The length of the canal measured along 

 the inferior root is about five millimetres. The length of the roof is greater, per- 

 haps nearly twice as much, but it is variable from the uncertain development of 

 that part of the bone ; definite dimensions are, therefore, wanting. The vertical 

 diameter, some five millimetres, of the opening into the orbit is a little greater than 

 the transverse. The small wing over- 

 hangs the front of the middle fossa 

 bounding the sphenoidal fissure above, 

 and ends laterally in a sharp point. The 

 anterior clinoid process is a sharp pro- 

 jection backward above the inferior 

 root and towards the posterior clinoid. 

 Sometimes it reaches the latter ; some- 

 times it is connected by a spur with the 

 middle clinoid process, then bridging the 

 carotid groove and making a carotico- 

 clinoid foramen (Fig. 211). The an- 

 terior border of the lesser wings is 

 rough at its inner part and smooth at 

 the outer, where it joins the posterior 

 edge of the horizontal plate of the frontal. The posterior border is smooth, form- 

 ing most of the boundary of the anterior and middle cranial fossae. 



The pterygoid processes'^ are downward projections which, articulating with 

 the palate bone, form the back of the framework of the upper jaw. Each consists of 

 two plates, an inner and an outer, united in front, diverging behind to form the 

 pterygoid fossa, and separating below on either side of the pterygoid notch. The 

 inner springs from the body, the outer from the great wing. The inner pterygoid 

 plate ^ is the longer. It is nearly vertical, ending in the slender haniular process"" 

 which points outward, bounding a deep little notch through which the tendon of the 

 tensor palati plays. At the inner side of its origin the internal plate presents a 



scale-like curved projection, the vaginal 

 process, above which is an antero-poste- 

 rior groove below the body of the sphe- 

 noid, in which the lateral expansion of 

 the base of the vomer is received. Just 

 external to the vaginal process is an- 

 other small groove, the pterygo-palatine , 

 which the palate bone converts into a 

 canal leading back from the spheno- 

 maxillary fossa. The outer pterygoid 

 plate ^ is broader and flares outward. 

 The anterior surface of the root is nearly 

 smooth, forming the back wall of the 

 spheno-maxillary fossa. It has the 

 openings of two canals : the upper and 

 outer is that of the foramen rotundum ; 

 the lower and inner, which is smaller, is 

 the Vidian canal, transmitting the nerve 

 and vessels of that name. There is a vertical ridge between the two, and a slight 

 groove below the latter, forming with the palate bone the beginning of the pos,te- 

 rior palatine canal which runs from the spheno-maxillary fossa through the hard 

 palate, transmitting a descending palatine nerve and vessels. The lower anterior 

 edges of both plates are rough to articulate with that bone. The outer surface of 

 the external plate is irregular for the origin of the external pterygoid muscle. The 

 inner wall of the inner plate is smooth. It bounds laterally the back of the nasal 

 cavity. The posterior borders of both plates are sharp, excepting that the inner is 

 formed by the union of two lines which enclose the scaphoid fossa where the tensor 

 palati arises. Rather less than half way down the Internal plate presents a promi- 



FlG. 



Spheno-maxillary fossa 



212. 

 Foramen ovale 



External 

 pterygoid 

 plate 



Foramen 



pterygo- 



spinosum 



Portion of sphenoid bone, showing the foramen pterygo- 

 spinosum. 



1 Foramen opticum. - Processus pterygoidei. ^ Lamina medialis proc. pteryg. ' Hamulus pterygtiidei. 

 t>roc. pteryg. 



' Lamina lateralis 



