THE FRONTAL BONE. 101 
constitute the external and internal angular processes respectively. The latter 
descend to a lower level than the former, and articulate with the lachrymal 
bones, being separated from each other by a rough articular surface—the nasal 
notch for the nasal and superior maxillary bones. The curve of the orbital 
margin varies in different individuals and races; towards its inner third it is 
crossed by a groove, not unfrequently converted into a foramen—the supraorbital 
notch or foramen (incisura sive foramen supraorbitalis). Through this there pass 
the supraorbital nerve and artery. Above the supraorbital margin the character 
of the bone displays marked differences in the two sexes: in the male, above the 
interval between the two internal angular processes, there is usually a well-marked 
prominence, called the glabella, from this the fulness extends outwards above the 
orbital margin, varying in degree and extent, and forming the elevations known as 
the supraorbital or superciliary ridges (arcus superciliares). The prominence of 
these naturally reacts on the character of the supraorbital margins, which are thicker 
and morerounded in the male than in the female. Passing upwards over the glabella, 
the remains of the suture which originally separated the two halvesof the frontal bone 
can usually be seen; above this point all trace of the suture is generally obliterated. 
Pacchionian Superior longitudinal 
For articulation with depression sinus and falx cerebri 
lesser wing of sphenoid AN | 
Orbital Date : : ; hs ese ag OY Surface for articula- 
4 y ‘ Vie i t Ly y i tion with great wing 
of sphenoid 
~Supraorbital notch 
4 
Ethmoidal notch Trochlear fossa 
Frontal sinus 
Nasal surface Nasal notch 
Nasal spine 
Fic, 78.—FRONTAL BONE AS SEEN FROM BELOW. 
Extending upwards from the external angular process is a well-marked ridge, 
which curves upwards and slightly inwards, then turning backwards it arches 
across the lateral aspect of the bone. This is the temporal ridge or crest (linea tem- 
poralis), which serves to separate the anterior surface of the frontal portion of the 
bone from its temporal aspect. The latter (facies temporalis) forms the floor of the 
upper and anterior part of the temporal fossa, and serves for the attachment of the 
temporal muscle. 
The orbital part of the bone (pars orbitalis) consists of two transversely-curved 
plates, each having the form of a sextant; their inner edges, which are cellular, lie 
parallel to each other, and are separated in their posterior half by the ethmoidal 
notch (incisura ethmoidalis), in which the ethmoid bone is lodged. The edges of 
the notch on either side are grooved in front and behind by the anterior and posterior 
ethmoidal foramina, which are completed when the ethmoid is in situ. The anterior 
transmits the internal branch of the nasal nerve and the anterior ethmoidal vessels ; 
the posterior, the posterior ethmoidal vessels. In front of the ethmoidal notch is the 
nasal notch, from the centre of which the nasal process projects downwards and for- 
wards to terminate in the nasal spine (spina nasalis), which lies between, and articu- 
lates with the nasal bones and perpendicular plate of the ethmoid. On either side 
of the root of this process the bone is grooved obliquely from above downwards and 
