102 OSTEOLOGY. 
forwards, and enters into the formation of the narrow roof (pars nasalis) of the 
nasal fossee. Anteriorly the nasal notch is hmited by a rough U-shaped articular 
surface, the median part of which articulates with the nasal bones, whilst on either 
side the nasal processes of the superior maxill are united with it. Behind this, 
amid the broken cells, the passages leading into the frontal sinuses are readily 
distinguished, and here the inner edges of the orbital plates articulate with the 
lachrymal bones. 
The orbital plate is thin and brittle. In front it is bounded by the superior 
orbital margin, just within which, midway between the internal angular process 
and the supraorbital notch there is a small shallow depression (fovea trochlearis), 
often displaying a spicule of bone arising from its edge (spina trochlearis), which 
affords attachment to the pulley of the superior oblique muscle of the eyeball. 
Externally the orbital plate is overhung by the orbital margin and the external 
angular process, and in the hollow so produced (fossa glandulze lachrymalis) the 
lachrymal gland is lodged. The extremity of the external angular process (pro- 
cessus zygomaticus) articulates with the frontal process of the malar bone. Behind 
this the irregular edge of the orbital plate is united with the great wing of the 
sphenoid by a triangular area, which also extends on to the inferior aspect of 
the temporal surface of the frontal bone. The apex of the orbital plate, for the 
space of about half an inch, articulates with the lesser wing of the sphenoid. 
The cerebral surface of the bone forms a fossa in which lie the fore and under 
parts of the frontal lobes of the cerebrum, the convolutions of which impress their 
form on the inner aspect of the bone. Here, too, on either side of the middle line, 
may be seen depressions for the lodgment of Pacchionian bodies. Descending from 
the centre of the upper margin of the bone is a vertical groove, the frontal sulcus ; 
narrowing below, this ends in a ridge—the frontal crest—which nearly reaches 
the fore part of the ethmoidal notch, where it terminates in a small orifice, the 
foramen crecum, placed usually in the suture between the fore part of the ethmoid 
and the frontal. This foramen may, or may not, transmit a small vein from the 
nose to the commencement of the superior longitudinal sinus. This sinus, which 
is interposed between the layers of the falx cerebri, is at first attached to the 
frontal crest, but subsequently occupies the frontal suleus. Deeply concave from 
side to side and from above downwards, the lateral aspects of the fossa are seen to 
be traversed by small grooves for the anterior branches of the middle meningeal 
arteries. Below, the orbital plates bulge into the floor of the fossa, so that the 
ethmoidal notch appears recessed between them. On either side of the notch faint 
grooves for the meningeal branches of the ethmoidal vessels may be seen. The 
circumference of the fossa is formed by the serrated edges of the bone which 
articulate with the parietals above, and on either side below with the great and 
lesser wings of the sphenoid. 
Connexions.—The frontal articulates with twelve bones, viz. posteriorly with the parietals 
and sphenoid ; externally with the malars; inferiorly and internally with the nasals, superior 
maxille, lachrymals, and ethmoid. 
Architecture.—The frontal bone is composed, like the other bones of the cranial vault, of 
two layers of compact tissue, enclosing between them a layer of spongy cancellous texture—the 
diploe. In certain definite situations, owing to the absorption of the intermediate layer, the 
bone is hollow, forming the frontal air sinuses. The position and extent of these is to some 
extent indicated by the degree of projection of the superciliary ridges, though this must not be 
taken as an absolutely reliable guide, for cases are recorded where the ridges were low and the 
sinuses large, and vice versa. Of much surgical importance, these air-spaces only attain their full 
development after the age of puberty, being of larger size in the male than in the female, a 
circumstance which accounts for the more vertical appearance of the forehead in woman as con- 
trasted with man. Usually two in number, they are placed one on either side of the middle 
line, and communicate by means of the infundibulum with the nasal fossa of the same side. 
It is exceptional to find the sinuses of opposite sides in communication with each other, as they 
are generally separated by a complete partition which, however, is occasionally much deflected 
to one or other side. Logan Turner (“On the Illumination of the Air Sinuses of the Skull, with 
some Observations upon the Surgical Anatomy of the Frontal Sinus,” Edin. Med. Jowrn. May 1898) 
gives the average dimensions of these sinuses as follows :—Height, 31 mm., z.e. from the fronto- 
nasal aperture upwards ; breadth, 30 mm., 7.e. from the septum horizontally outwards ; depth, 17 
mm., from the anterior wall at the level of fronto-nasal suture backwards along the orbital roof. 
Exceptionally large sinuses are sometimes met with extending backwards over the orbit so as to 
form a double roof to that space. There is a specimen in the Oxford collection in which the 
