728 



CRANIUM. 



into the angle of the petrous and squamous 

 portions of the temporal bone. The laxator 

 tympani muscle arises from this process, and 

 the sti/loid process before described descends 

 from it. The angle which exists where this 

 border departs from the body, in part forms the 

 foramen laceriiin antcrius, an opening which, 

 in the recent skull, is closed by cartilage. 



The anterior border consists of two portions 

 which join with each other at an angle. Of 

 these the upper is indented, separates the or- 

 bital from the temporal surface, and articulates 

 with the malar bone. The inferior portion is 

 smooth, and forms with the palatine and supe- 

 rior maxillary bone, the Jissura lacera orbitalis 

 inferior. 



The alte. minores are on the upper and an- 

 terior part of the body of the bone ; they ex- 

 tend outwards over the superior borders of the 

 greater wings, and, gradually tapering, they at 

 last end in a point. 



The upper surface of eachala minor is smooth, 

 and partly forms the anterior fossae of the skull. 

 The processus etlnmtidulls is a thin lamina 

 somewhat triangular in form, prolonged for- 

 wards on the median line to articulate with the 

 cribriform plate of the ethmoid bone. Passing 

 backwards from this process, there is a slightly 

 elevated line separating the depressions which 

 on each side receive the olfactory nerves, and 

 terminated posteriorly by a tubercle (processus 

 olivaris) marking the decussation of the 

 optic nerves, and having upon it a transverse 

 depression for the lodgement of their com- 

 missure. This depression terminates on each 

 side in the foramen optic urn for the passage of 

 the optic nerve and the ophthalmic artery, in 

 such a manner that the lesser ala appears to arise 

 by two roots, one above and the other below 

 the foramen. From the sides of the processus 

 ethmoidalis there pass the two transverse, spi- 

 tious processes, being the anterior serrated mar- 

 gins of the wings ; they are articulated to the 

 orbitar processes of the frontal bones, and 

 sometimes join by their extremities the great 

 wings ; thereby, in such a case, converting the 

 superior orbital fissure into a foramen without 

 the aid of the frontal bone. The posterior 

 margins of the alse minores are smooth and 

 iess sharp than the anterior ; they are pro- 

 longed backwards and inwards, so as to form 

 on each side a short and thick triangular pro- 

 cess, the apex being directed backwards, called 

 the anterior epftippial (anterior clinoid) pro- 

 cess, to which the cornua of the lunated margin 

 of the tentorium are attached. 



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 Jissura 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 foramen lacerum orbitale super ius, 

 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 ophthalmic veins. 



The articulations then of this bone are, to 

 the ethmoid, by the ethmoidal 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 ofintra-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 

 points of 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 between 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 they 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. TheJ'rontalbone(osfrontis, corona; Germ. 

 das StirnbeinJ (F, jig. ! 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- 



