CRANIUM. 



729 



work, which will be afterwards more fully ex- 

 plained. The convexity of these domes is turned 

 outwards and forwards in such manner that the 

 circumference may abut against the longitu- 

 dinal rib internally ; and, behind against the 

 anterior rib in the base and a portion of the 

 circumference of the lateral dome in the vault. 

 That portion which is in the base is, as it were, 

 pressed upwards to increase the space of the 

 orbit, but not so much so as, at first sight, 

 might appear; for on the external surface of 

 the junction of the two portions there is an 

 extraordinary development of the bone, which 

 projecting over the face destroys the uniformity 

 of surface and causes the orbitar portion to 

 appear more elevated than it is in reality, and 

 even to pass backwards at right angles with 

 the other. 



Fig. 372. 



The external surface of the frontal portion 

 in its upper two-thirds is smooth, of an equa- 

 ble convexity and directed backwards; its 

 inferior third is more vertical, and its convexity 

 is interrupted by prominences. On the me- 

 dian line it exhibits evidence of its original 

 division into two parts, and this generally by 

 a slight ridge, although in some instances there 

 is a linear depression of equal indistinctness. 

 This line is terminated by the nasal prominence, 

 which has immediately above it a smooth tri- 

 angular surface (glabella), and below it a 

 rough notch for the articulation of the nasal 

 and superior maxillary bones. From the 

 centre of this notch there is a projection (pro- 

 cessus nasalis), on the fore part of which are 

 fixed the nasal bones, and to its back part, 

 which is grooved, the ethmoid bone is ap- 

 plied. 



On either side of the median line there is, 

 at about the distance of an inch where the 

 middle joins with the lowest third of the bone, 

 the frontal eminence ( eminent ia front alis, pro- 

 cessus prinii genii), which marks the centre 

 of ossification, and the prominence of which 

 is inversely as to the age of the subject. Be- 

 low this eminence, bounding the glabella, and 

 inclining downwards and inwards towards the 

 nasal prominence (with which, in fact, it is 

 ultimately confounded), is a pyramidal protu- 

 berance, varying very much in distinctness in 



VOL. i. 



different individuals, (processm frontalis,) 

 more evident below than above, and indicating 

 the situation of the frontal sinus. There is a 

 slight depression underneath and to the outer 

 side of this process, and, finally, the super- 

 ciliary ridge terminates the frontal portion of 

 the bone. This ridge is more prominent at its 

 outer than at its inner side ; its extreme points 

 are called external and internal angular pro- 

 cesses, to the former of which the malar bone 

 is articulated, to the latter the os unguis; at 

 the junction of its inner and middle thirds 

 there is a hole (foramen supra orbitarium), 

 or otherwise a notch, for the passage of the 

 frontal branch of the ophthalmic vessels and 

 of the ophthalmic division of the fifth pair of 

 nerves. Behind the external angular process 

 there is a depression (fossa temporalis) which 

 forms part of the temporal fossa ; a part of the 

 temporal muscle is attached to it, and it is 

 bounded above by a line (linea temporalis) 

 which is continuous with the outer margin of 

 the external angular process, and to which is 

 attached the temporal aponeurosis. 



Fig. 373. 



The posterior or cerebral surface of the 

 frontal bone is concave, is marked by depres- 

 sions which correspond with the convolutions 

 of the brain, and by sulci for the lodgement of 

 the arteries of the dura mater, and is conti- 

 nuous inferiorly with the orbitar portion ; cor- 

 responding to the eminentiae frontales there are 

 two depressions, and on the median line there 

 is a sulcus (sulcus longitudinalis) for the re- 

 ception of the longitudinal sinus, on the edges 

 of which sulcus may sometimes be seen the 

 fossae Pacchionii for the glands of the same 

 name. This sulcus as it descends is generally 

 replaced by a dense crest, which projects con- 

 siderably into the cavity of the cranium; to it 

 and to the edges of the sulcus, the falx cerebri 

 is attached ; and at its lowest point it is bifid, 

 so that, by its being applied against a similar 

 bifurcation of the processus cristatus of the 

 ethmoid bone, it contributes to form t\\c fora- 



men 



3 n 



