THE BONES OF THE HEAD 67 



on the under aspect there is a rough, semilunar, serrated surface 

 for articulation with the nasal bones and nasal processes of the 

 superior maxillae, and behind this is the nasal notch, bounded at 

 either side by the internal angular process. Within the notch is 

 the nasal process, which supports the nasal bones, and projecting 

 downwards from it is the sharp nasal spine, which articulates in 

 front with the upper part of the crest of the nasal bones, and behind 

 w th the vertical plate of the ethmoid. This spine enters into the 

 nasal septmn. On either side of the spine is the ala, which is 

 grooved to take part in the roof of the corresponding nasal fossa. 



The internal or cerebral surface of the frontal portion is concave, 

 and in the middle line presents a groove, called the frontal sulcus, 

 which lodges a part of the superior longitudinal venous sinus. 

 On either side of the upper pait of this groove there are a few 

 depressions for the Pacchionian bodies. In'eriorly the groove is 

 replaced by the frontal crest, which terminates at the foramen 

 caecum. This foramen is sometimes partly formed by the crista 

 galli of the ethmoid, and it may be closed below, or it may transmit 

 an emissary vein, which passes between the intracranizd superior 

 longitudinal sinus and the veins of the roof of the nose. The 

 internal surface presents numerous digitate impressions for the 

 convolutions of the frontal lobes of the cerebrum, and laterally 

 there are a few meningeal grooves, transversely disposed, for 

 branches of the middle meningeal arteries. 



The supero-laiera! or parietal border of the frontal portion is 

 serrated for the parietal bones. Superiorly it is slightly bevelled 

 near the middle line at the expense of the inner plate, where it over- 

 laps the parietal, and at either lower extremity it is distinctly 

 bevelled at the expense of the outer plate, where it is overlapped 

 by the parietal. Internal to its lower termination at either side 

 there is a rough triangular surface, which is serrated for the great 

 wing of the sphenoid. 



The orbit^ plates, thin and brittle, project backwards in a 

 curved manner from the supra - orbital arches, and are widely 

 separated by the ethmoia^ 1 notch, which is occupied by the cribri- 

 form plate of the ethmoid. Each is triangular, with the truncated 

 apex directed backwards and inwards, and presents two surfaces 

 and three borders. The superior or cerebral surface is irregularly 

 convex, and marked by digitate impressions for the convolutions 

 of the orbital surface of the frontal lobe, which rests upon it. 

 The inferior or orbital surface, smooth and concave, forms the 

 principal part of the roof of the orbit. Within the external angular 

 process is the lachrymal fossa, which lodges the lachrj-mal gland, 

 and near to the internal angular process is the small trochlear fossa, 

 which gives attachment to the trochlea of the superior oblique 

 muscle of the eyeball. 



The borders are anterior, external, and internal. The anterior 

 border represents the supra-orbital arch, and is free. The external 

 border is sharp and irregular, and its diiection is backwards and 



