CRANIUM. 



727 



placed with such a degree of obliquity, that it 

 may be questioned whether it be on the posterior 

 or superior surface of the body of the bone. It 

 is smooth, slightly concave, and on its edges 

 may often be seen the commencement of the 

 sulci basiltires for the lodgement of the basilar 

 sinuses. 



The ala. majores are those large curved pro- 

 cesses, which, stretching outwards, forwards, 

 and upwards, contribute to form the middle 

 fossae of the skull, the orbits, and the temples. 

 The upper surface of each ala, that which in 

 part forms the middle fossa of the base of the 

 skull, is concave from side to side, and still 

 more so from behind forwards. On it are seen 

 (though not so distinctly) the digital impres- 

 sions which mark the lodgement of convo- 

 lutions of the brain on the cerebral surface of 

 the other bones of the skull. Close to the spot 

 where it departs from the body of the bone 

 there is a sulcus directed forwards, and ter- 

 minating in a round hole (foramen rotund um) 

 for the exit of the superior maxillary branch 

 of the par trigeminum or fifth pair of nerves. 

 More outwardly, and behind the plane of 

 the posterior edge of the body of the bone, 

 is a large oval opening (foramen ovale), di- 

 rected downwards and slightly outwards for the 

 transmission of the inferior maxillary branch 

 of the par trigeminum and the entrance of the 

 ascending pharyngeal artery, which then be- 

 comes a meningeal vessel. Behind this fora- 

 men is another (the foramen spinale), which is 

 very small, and affords entrance to the middle 

 meningeal artery. 



On the Inferior surface are seen the pterygoid 

 processes descending from the great wing where 

 it joins the body of the bone, to afford a resist- 

 ing surface against which the bones of the face 

 may be grouped. Anterior to these processes 

 is the termination of the foramen rotundum, the 

 opening of which is directed somewhat out- 

 wards, and from which there passes, outwards 

 and upwards, a groove (sulcus temporalis) for 

 a deep temporal branch of the superior maxil- 

 lary nerve. Behind the pterygoid processes, 

 and extending from the base of the internal to 

 the extremity of the wing, is the sulcus Eusta- 

 c/iianus, which lodges part of the Eustachian 

 tube, and on the outer side of this sulcus are 

 seen successively the foramen ovale and the 

 foramen spinale. Immediately behind the lat- 

 ter opening, and overhanging the Eustachian 

 tube, is the styloid process, to which the inter- 

 nal lateral ligament of the lower jaw is attached. 

 On the outer side of the pterygoid processes is 

 a plain surface forming part of the zygomatic 

 fossa, and bounded externally by a crest, which 

 marks the division between the zygomatic and 

 the temporal fossae, and which intervenes be- 

 tween the superior attachment of the external 

 pterygoid and the inferior attachment of the 

 temporal muscles. 



The pterygoid processes consist of two 

 plates, with a triangular separation inferi- 

 orly, and they are called the external and the 

 internal pterygoid processes or plates. The 

 external is broader, thinner, and is directed 



more outwardly than the internal ; its outer 

 surface, which also looks a little forwards, 

 gives attachment to the external pterygoid, its 

 inner to the internal pterygoid muscles. The 

 internal is nearly vertical ; it is pierced longi- 

 tudinally at its base by the canalis Vidianus 

 for the passage of the vessel and nerve which 

 bear that name ; at its inferior extremity there 

 is a hook (the haynular process), which acts 

 as a pulley for the tensor palati muscle, the 

 attachment of which to the outer side of the 

 internal pterygoid process is shewn by a sul- 

 cus which is most evident at the base (fossa 

 navicularis) ; to its anterior edge is applied a 

 thin plate of the palatine bone, thus sepa- 

 rating it from the superior maxillary, and to 

 its posterior edge is affixed the aponeurotic 

 origin of the superior constrictor of the pha- 

 rynx. The concavity between the two pro- 

 cesses is the fossa pterygoidea which is occu- 

 pied by the internal pterygoid muscle, and 

 the notch at the lower part (the hiatus pala- 

 tinus) is filled up by the pterygoid process of 

 the palatine bone. 



The external surface of each ala is continu- 

 ous with the inferior ; it is concave from before 

 to behind, and convex from above downwards ; 

 it contributes to the formation of the temporal 

 fossa, and the continuation of the sulcus tem- 

 poralis is evident at its anterior part (S, Jig. 

 373). 



The anterior surface forms the major part of 

 the external wall of the orbit, is oblong, di- 

 rected forwards and inwards, and is narrower 

 at its extremities than in its middle. 



The superior border of the great wing sepa- 

 rates the orbital from the cerebral surface ; it 

 presents a sharp smooth edge on its inner half, 

 and a rough irregular surface on its outer half; 

 it is convex, and its convexity is directed up- 

 wards, forwards, and inwards. The sharp 

 internal half concurs with the alae minores to 

 form the sphenoidal fissure, which will be de- 

 scribed with those processes. The external 

 rough half becomes broader as it passes out- 

 wards, so as to produce a triangular indented 

 surface, the outer edge of which is prolonged 

 at the expense of the inner table in such a 

 manner that it overlaps the frontal bone which 

 is affixed on it, and this prolongation is con- 

 tinued without the indented surface, so as to 

 grasp the anterior inferior spinous process of 

 theparietal bone. 



The external border is nearly the reverse of 

 the former. It is concave, and looks outwards 

 and backwards, and it is articulated in its entire 

 extent to the squamous portion of the temporal 

 bone, by which it is overlapped in its anterior 

 third, and receiving and supporting it in its 

 two posterior thirds ; the former at the expense 

 of its outer table, the latter at that of the in- 

 ternal. 



The posterior border is applied against the 

 outer side of the petrous portion of the tem- 

 poral bone, and extends from the body of the 

 sphenoid to the posterior extremity of the ex- 

 ternal border. The junction of these two bor- 

 ders forms the spinous process, which is received 



