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projects downwards a vertical plate of bone, the external 

 pterygoid process, connected along its inner edge with the 

 palatine bone. 

 (3) The parietals, meeting at the sagittal suture, and forming a 

 large part of the roof of the cranial cavity. 



(The inter-parietal, a small irregularly lozenge-shaped 

 bone, lies between the parietals and the supra-occipital.) 

 (c) The frontal segment. Note — 



(1) The pre-sphenoid, a small laterally compressed bone, in 



front of the basi-sphenoid, forming the lower margin of the 

 optic foramen, from which it extends backwards to form 

 the anterior boundary of the sella turcica, and forwards to 

 form two thin vertical blades, diverging from each other 

 to form part of the inner wall of the orbit. 



(2) The orbito-sphenoids, a pair of plate-like bones, fused with 



the pre-sphenoid, and surrounding the optic foramen, behind 

 which they form part of the wall of the cranium and of the 

 orbits. 

 (3) The frontals, forming the roof and sides of the anterior part 

 of the cranial cavity, and the upper part of the wall of the 

 orbit, each bearing a prominent supra-orbital process, and 

 articulating with each other in the middle line, with the 

 parietal behind, and with the orbito-sphenoid and pre- 

 sphenoid below. 

 \^d) The nasal or olfactory segment. Note— 



(1) The mesethmoid, a median vertical plate of cartilage, 



extending downwards and forwards in front of the pre- 

 sphenoid, having its upper and posterior border ossitied and 

 expanded horizontally to form the perforated cribriform plate. 



(2) The nasals, a pair of elongated bones forming the roof of 



the nasal cavities, articulating with each other in the 

 middle line, and with the frontals posteriorly. 



(3) The ethmo-turbinals, intricately folded plates of bone, fused 



to the lower surface of the cribriform plate. 



(4) The maxillo-turbinals, more delicate and more complex bones 



attached to the maxillse in front of the ethmo-turbinals. 



(5) The naso-turbinals, thin bones forming pouches and fused 



with the inner surfaces of the nasal bones. 



(6) The vomers, a pair of slender plate-like bones fused along 



their ventral margins, and embracing the lower edge of the 

 mes-ethmoid cartilage, and connected posteriorly with the 

 ethmo-turbinals. 

 Note the lacrymals, small plate-like bones, indirectly connected with the 



nasal capsules. They form part of the anterior walls of the orbits, 



and articulate with the frontals and maxillte. 



