38 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



The Frontal Bone 



The frontal (from, forehead) arches up and back above the 

 orbits, forming the forepart of the cranium. It articulates 

 with twelve bones the parietals and sphenoid, the malars, 

 the nasals, superior maxillae, lacrymals, and ethmoid. It 

 consists of two portions, a superior vertical or frontal and 

 an inferior horizontal, and presents three surfaces, anterior, 

 inferior, and cerebral which is continuous in the two portions. 



The anterior surface shows the greatest convexity on each 

 side in the frontal eminence, separated by a slight depression 

 below from the superciliary ridge, just above the orbit. In 

 the middle line between the two ridges is a smooth surface, 

 the glabclla (without hair), also called nasal eminence. The 

 orbital arch ends in extremities called the internal and external 

 angular processes; the internal is slightly marked, and articu- 

 lates with the lacrymal bone; the external is prominent, and 

 articulates with the malar. At the junction of the inner and 

 middle third of the arch is the supraorbital notch or foramen 

 for the supraorbital nerve and vessels. The temporal crc^t 

 springs from the outer angular process, and is continuous with 

 the inferior temporal line on the parietal. Inferiorly are two 

 thin horizontal laminae, the orbital plates, forming the roof 

 of the orbits and separated by the cthmoidal notch. 



Inferior Surface. The orbital plates are somewhat tri- 

 angular, with their internal margins parallel. Close to the 

 external angular process is the lacrymal fossa, and close to 

 the inner process is the trochlear fossa for the pulley of the 

 superior oblique. Between the internal angular processes 

 is the nasal notch, and from its concavity the nasal process 

 projects beneath the nasal bones and nasal processes of the 

 superior maxillae, and supports the bridge of the nose. On 

 the posterior surface of this process are two grooves which 

 enter into the roof of the nasal fossae; between the grooves is 

 a median ridge, the nasal spine, which descends in the septum 

 of the nose above the perpendicular plate of the ethmoid. 

 Along the inner margins of the ethmoidal notch are irregular 

 depressions forming the roof of cells in the ethmoid. Each 

 border is marked inferiorly by two grooves, completing with 

 the ethmoid the anterior and posterior internal orbital canals; 



