The inferior surface of each ala minor forms the posterior part of the orbit. On it is seen the opening of the optic foramen, and under neath it, between the smaller and the greater wings, the fissura lacera orbitalis superior. This fissure is completed into a foramen by the articulation of the frontal bone to the sphenoid, when it appears as an elongated triangular opening directed from below up wards and from within outwards. Thus is formed the foranien lacerum orbitale superius, which allows to emerge from the skull the third, fourth, the ophthalmic division of the fifth, and the sixth pair of nerves, and to enter from the orbit the ophthalinic veins.
The articulations then of this bone are, to the ethmoid, by the etlimoidal process and the fore part of the body; to the frontal, by the transverse spinous processes, and the summits of the great wing; to the parietal, by the tips ; to the temporal, by the external and posterior borders, and to the malar, by the anterior bor ders of the same wings ; to the occipital, by the basilar process ; to the palatine, by the ptery goid processes and adjacent part of the body ; and to the vomer, by the azygos process.
The sphenoid bone is developed by nu merous points of ossification, some of which coalesce before the others appear ; and during the period of intra-uterine life the union of these parts is so rapid, that, at birth, the bone con sists but of three parts, one central, compre hending the body and smaller wings, and two lateral, each involving a great wing and its cor responding pterygoid processes.
So early as the third month there appear six pointsjof ossification, two in the great wings, two in the internal pterygoid processes, and two in the smaller wings. During the fourth, fifth, and sixth months six points are esta blished in the body, one on each side the median line, afterwards another between these and the corresponding greater wing, and ulti mately another between the optic foramen and those already existing. During the sixth month also a deposit appears between the optic fora men and the olivary process. In the course of the seventh month the six points of ossification in the body run into each other; in the next month a coalition takes place between those in the pterygoid processes and those in the greater wings, and shortly afterwards a similar union occurs beti,veen the point in the small , wing and that near the optic foramen. To wards the termination of the ninth month the two smaller wings are associated together, which then become attached to the already formed body, and thus constitute at birth the three pieces which exist at that epoch.
In the early period of extra-uterine life these three portions unite into one, the great wings acquire a more determined curvature than tbey at first possessed, the pterygoid pro cesses lose their striated appearance, and ex hibit more completely their fossa ; but it is not until after the lapse of years that the ab sorbing process, which, commencing in the centre of the body, developes the sinuses, is terminated, so that during childhood there is not only an absence of these sinuses, but of the openings leading from them and of the tur binated processes which are, fixed to their front.
2. Thefrontal bone ( osfrontis, corone e ; Germ. das Stirnbein,) (F, fig. 370, 373,) is situated at the anterior part of the cranium, forming part of the vault and part of the base, but considerably more of the former than it does of the latter. It comprises the two anterior ovoidal domes and the anterior portion of the longitudinal curved rib of the general frame 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.
different individuals, (processus 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 interrutl angular prc 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 (foranien 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 Obssa temporalis) which forms part of the temporalftssa ; 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 attac.hed the temporal aponeurosis.