THE SPHEXOrn 



33 



thin, forms by its outer surface tlie iiuier wall of the zyjromatic fossa, tind affords 

 attaehuicut to the external pten/(/oid nuiscle. From its imu-r surface the internfd 

 pterj/goid takes origin. 



The internal pterygoid plate is narrower and longer than the external. Its 

 inner surface forms part of the outer l)0undary of the nasal fossa, and l)y a thin 

 li'dge of bone, called the vaginal process, extends to the under surface of the basi- 

 sphenoid to articulate with the ala of the vomer, and anteriorly with the sjilicnoidal 

 process of the palate bone. Inunediately al»ove this ledge of Ixme is the pterygo- 

 palatine groove (converted into a canal by the si)henoidal j)roeess of the palate 

 bone), for an artery and nerve (»f the same name. At the point where the internal 

 pterygoid plate conies into relation with the great wing and the lingula, there is the 

 Vidian canal. This canal is 3 cm. long, and transmits the Vidian nerve and 

 artery. The outer surface of the internal pterygoid plate forms the inner boundary 

 of the pterygoid fossa ; its -posterior border is prolonged into a hamular process, 

 smooth on its under aspect, for the bursa between it and the tensor (cireumflexus) 

 palatl. From the lower third of the posterior border and the hamular process the 

 (<iij)erior constrictor of tlie ])harvnx takes origin. 



The anterior borders of these processes diverge below, and have rough edges for 

 articulation with the tul)erosity of the palate Ixme; the gap between them is the 

 pterygoid notch. Superiorly, the pterygoid ])rocesses form a triangular surface, 

 which constitutes the posterior boundary of the spheno-maxillarv fossa, and presents 

 above the anterior orifice of the Vidian, and more internallv the commencement of 



Fig. 40.— Thk L'ndei: Sikiwce of Pkk-Sphenoid at the Sixth Year. 



PTERYGO-PALATiNE GROOVE 



OPTIC FORAMEN 



ViD.AN CANAL 

 VAGINAL PROCESS 



the ]>terygo- palatine canal. The anterior border of the internal pterygoid ]>late 

 articulates with the posterior ])order of the vertical ])late of the )»alate bone. 



The recess between thetwo ])terygoid ])lates posteriorly is subdivided. Theu]>i)er, 

 smaller and shallower depression is the scaphoid fossa; it gives attachment to 

 the tensor (cireumflexus) palatl externally, and the cartilage of the Eustachian tube 

 internally. The lower, deeper and larger, is the pterygoid fossa; it lodges the 

 internal jttenjgoid and tensor piditti muscles. The fossa is comi)lete(l l)y the tuber- 

 osity of the ])alate bone. 



Articulations. — The sphenoid articulates with the following Itones: ethmoid, 

 frontal. i)arietal, temporal, epipteric, palate, vomer, occipital, malar, sphenoidal 

 turbinals, and occasionally with the maxilla. 



Muscles. — It gives origin to the following nniscles: — 



Tem])oral. 

 Internal jttervgoid. 

 External pterygoid. 

 Tensor tympani. 

 Tensor palati. 



External rectus of the eyeball. 

 Internal rectus '' " 



Su))erior rectus " " 



Superior oblique " " 



Levator palpebrte. 



Ligaments. — The sphenoid has numerous intrinsic ligaments which occasion- 

 ally ossify and produce adventitious foramina. Of these, the more important 

 are: — 



Inter-dinoid. — This passes fr<»iii the anterior to the posterior clinoid processes. 

 3 



