2oo Anatomy of Skeleton 



The front surface presents : 



(a) Two frontal eminences, marking the site of commencing ossification and 

 due to the fixation of the earlier curves as a result of this. 



(b) Supmorbital ridges meeting centrally and fading away above the middle 

 of the orbital margins due for the most part to the existence of the frontal sinus, 

 a large air sinus situated here between the two tables of the bone. Covered by 

 Orbicularis laterally and Occipito-frontalis centrally, and giving origin to fibres 

 of Corrugator supercilii that run out to join the deep surface of Orbicularis. 



(c) On the orbital margin the supraorbital notch for these vessels and nerve : 

 sometimes, as in the figure, this is closed and converted into a foramen by ossifica- 

 tion of a " supraorbital ligament " that crosses the notch. In the floor of the notch 

 may be seen a small canal for minute vessels and nerve to the frontal sinus. The 

 orbital margin ends externally in the external angular process : it is less sharply 

 marked at its inner end, presents an ill-defined groove here for the supratrochlear 

 nerve, and turns down as the internal angular process at the side of the nasal 

 surface. It has the superior palpebral ligament attached to its outer part. 



(d) The metopic suture, always to be found between the supraorbital ridges, 

 and occasionally (7 or 8 per cent. Europeans) completely separating the two halves 

 of the bone : the complete fissure occurs in only i per cent, of African skulls, 

 and 4 or 5 per cent, of skulls of yellow races. 



The temporal surface (Fig. 166) is separated from the frontal surface by the anterior 

 part of the superior temporal crest, running down to the external angular process : 

 it gives origin to fibres of Temporal muscle. A large part of the superficial aspect 

 of the bone here is articular, being overlapped by the parietal above and the great 

 wing of sphenoid below. 



The orbital surface of each orbital plate (Fig. 166) is deeply concave, and triangular 

 in shape with the blunted apex pointing backwards and inwards ; this accords with the 

 pyramidal shape of the orbital cavity, which forms an apex behind and internally, 

 at the optic foramen. As the orbital plate makes the greater part of the roof of the 

 cavity its general shape is therefore triangular, but its apex is cut off because the lesser 

 wing of sphenoid forms the roof of the apical part of the cavitj'. The surface is in 

 contact with the upper surface of the Levator palpebrae and Superior oblique muscles 

 and the orbital fat and the supraorbital vessels and nerve and supratrochlear nerve, 

 and presents : 



(a) Hollow for lodging the lachrymal gland. 



(b) A depression, sometimes a small tubercle, that marks the attachment of 

 the pulley of the Superior oblique the trochlear fossette. 



(c) Notches on its inner margin that mark the position of the anterior and 

 posterior orbital (ethmoidal) foramina, completed by the articulation with the 

 ethmoid. 



Notice that the inner borders of the surfaces are practically parallel, while the outer 

 ones, if prolonged, would meet at a right angle : compare this with the orbit in the skull. 



The inner margins are connected by the nasal part of the bone in front, but they 

 are separated in their posterior half or more by the ethmoidal notch ; this is filled by the 

 ethmoid in the complete skull. Observe that the ethmoid lies below the level of the 

 orbital plates, which rest on it, so that there is a rough articular surface running along 

 the margins of the notch, for the ethmoid. This ethmoidal surface comes forward to 



