95 



are seen the alae of the vomer. On the under surface of the vaginal process is a 

 groove (sulcus pteryyopalatinus), which in the articulated skull is converted into 

 the pterygopalatal canal by union with the sphenoidal process of the palate bone. 

 At the junction of the vaginal process and the inner plate is the pterygoid tubercle, 

 just above which is the posterior opening of the Vidian canal. The anterior 

 surface of the pterygoid process is quite broad at its base, and forms chiefly the 

 posterior wall of the sphenomaxillary fossa. 



The Sphenoidal Turbinated Processes (conchae sphenoidales). The sphe- 

 noidal turbinated processes are two thin curved plates of bone, which exist as 

 separate pieces until puberty, and occasionally are not joined to the sphenoid 

 in the adult. They are situated at the anterior and interior part of the body 

 of the sphenoid, an aperture (apertura sinus sphenoidalis] of variable size being 

 left in the anterior wall of each, through which the sphenoidal sinuses open into 

 the nasal fossae. They are irregular in form and taper to a point behind, being 

 broader and thinner in front. Their upper surface, which looks toward the 

 cavity of the sinus, is concave; their under surface convex. Each bone articulates 

 in front with the ethmoid, externally with the palate; its pointed posterior 

 extremity is placed above the vomer, and is received between the root of 

 the pterygoid process on the outer side and the rostrum of the sphenoid on the 

 inner. 1 



Development. Up to about the eighth month of fetal life the sphenoid bone consists of two 

 distinct parts a posterior or postsphenoid part, which comprises the sella turcica, the greater 

 wings, and the pterygoid processes; and an anterior or presphenoid part, to which the anterior 

 part of the body and lesser wings belong. It is developed from fourteen centres eight for the 

 postsphenoid division and six for the presphenoid. All parts except the internal pterygoid 

 plates have an intracartilaginous origin. 



Postsphenoid Division. The first nuclei to appear are those for the greater wings (ali- 

 sphenoids). They make their appearance between the foramen rotundum and foramen ovale 

 about the eighth week, and from them the external pterygoid plates are also formed. Soon after, 

 the nuclei for the posterior part of the body appear, one on either side of the sella turcica, and 

 become blended together about the middle of fetal life. About the ninth or tenth week the 

 centre for the internal pterygoid plate 'appears, followed by the centre for the hamular process; 

 the centre for the lingula appears during the fourth month, and soon joins the rest of the body. 

 The.internal and external pterygoid plates become joined at about the sixth month. 



one for each two for anterior 

 lesser wing, part of body. 



I A 



one for each internal,---' 1 ' j 

 pterygoid plate. '' ne 



one for f or each lingula. \ 



each greater wing and external ptery- 

 [goid plate, 

 one for each Sphenoidal turbinated process. 



FIG. 60. Plan of development of the sphenoid. 

 From fourteen centres. 



FIG. 61. Sphenoid bone at birth. Posterior aspect. 



Presphenoid Division. The first nuclei to appear are those for the lesser wings (orbito- 

 sphenoids). They make their appearance about the ninth week, at the outer borders of the optic 

 foramina. A second pair of nuclei appears on the inner side of the foramina shortly after, and, 

 becoming united, form the front part of the body of the bone. The remaining two centres for 



1 A small portion of the sphenoidal turbinated process sometimes enters into the formation of the inner 

 wall of the orbit, between the os planum of the ethmoid in front, the orbital plate of the palate below, and 

 the frontal above. Cleland, Roy. Soc. Trans., 1862. 



