THE FRONTAL BONES 59 
parietal suture is usually closed at four years, the parieto-occipital at five years, and 
the squamous at twelve to fifteen years. 
THE FRONTAL BONES 
The frontal bones (Ossa frontalia) are situated on the limits of the cranium 
and face, between the parietals behind and the nasal bones in front. Each is 
irregularly quadrilateral, and consists of naso-frontal, orbital, and temporal parts. 
The naso-frontal part (Pars naso-frontalis) forms the basis of the forehead. 
Its external or frontal surface (Facies frontalis) is nearly flat, and is smooth and 
subcutaneous; it is separated from the temporal part by the external frontal crest 
(Crista frontalis externa). At the junction with the orbital part the supraorbital 
or zygomatic process (Proc. zygomaticus) curves outward and downward to join 
the zygomatic arch. The process partially separates the orbit from the temporal 
fossa; its root is perforated by the supraorbital foramen (Foramen supraorbitale), 
or presents instead a notch on its anterior border; its upper surface is convex, while 
the orbital surface is concave and smooth, forming a shallow fossa for the lacrimal 
Fic. 37.—Lerr Frontat Bone oF New-Born Foart; VENTRO-MEDIAL VIEW. 
A, Cerebral surface; B, B, orbital part; C, temporal part; D, nasal surface; 1, surface of junction with opposite 
bone; 2, frontal sinus; 3, ridge to which cribriform plate of ethmoid bone is attached; 5, fissure into which orbital wing 
of sphenoid bone fits; 6, sphenoidal notch; 7, supraorbital process; 8, junction with nasal bone; 9, junction with pari= 
etal bone; 10, junction with squamous temporal bone. 
gland (Fossa glandulse lacrimalis). The internal surface enters into the formation 
of the cranial and nasal cavities. The two plates of the bone separate and diverge 
in front, and thus inclose a large air-space which is part of the frontal sinus. The 
internal plate curves downward and forward and joins the cribriform plate of the 
ethmoid. Beyond this it inclines upward and joins the external plate at the naso- 
frontal suture. The cerebral surface presents digital impressions for the cerebral 
gyri. The nasal surface is longitudinally grooved. The external plate extends 
forward and joins the nasal and lacrimal bones. 
The orbital part (Pars orbitalis) forms the major part of the medial wall of the 
orbital cavity. It is separated from the naso-frontal part by a prominent ridge 
which is part of the orbital margin. Its orbital surface (Facies orbitalis) is concave 
and smooth, and presents superiorly a small depression (Fovea trochlearis), which 
is bridged by a small bar of cartilage, around which the superior oblique muscle of 
the eye is reflected. The lower border concurs with the orbital wing of the sphenoid 
in the formation of the ethmoidal foramen. The nasal surface faces into the 
frontal sinus and is to a small extent united with the lateral mass of the ethmoid. 
The temporal part (Pars temporalis) is separated from the orbital part by the 
