THE CKANIUM. 13*73 



In an antero-posterior skiagram of the skull, the light shadows formed by the 



i ethmoidal cells are seen to occupy the well-defined area bounded on either side by 

 the still lighter shadow of the orbital cavities and above by the dense horizontal 



.shadow of the cribriform plate, which occupies the frontier line between these 

 sinuses and the frontal sinuses. Anteriorly the ethmoidal area is overlapped 

 by the vertical shadow caused by the frontal processes of the maxillse and by 

 the ridges of the lacrimals. Not infrequently the ethmoidal cells will be seen to 

 extend into the roof of the orbit, while inferiorly and laterally they come into close 



'relation to the superior and medial angle of the shadow formed by the maxillary 

 sinus. The comparative transparency of the area of the ethmoidal cells is 

 accounted for by the fact that it is superimposed upon that of the sphenoidal 

 sinuses. 



In a profile skiagram the ethmoidal area is seen to extend from the frontal 

 process of the maxilla backwards across the orbits to the sphenoidal sinuses, with 

 which they are contiguous. This area is crossed about its middle by the vertical 

 shadow caused by the lateral margin of the orbit. In front of this, and occupying, 

 therefore, the light area of the orbital cavity, are the anterior ethmoidal cells ; while 



: behind it are the posterior ethmoidal cells. In a profile view of the skull, the 

 posterior ethmoidal cells, the sphenoidal sinuses, and the hypophyseal fossa all lie 



i from before backwards in the axis of those rays which pass through the thinnest 

 portion of the cranial box, namely, the anterior part of the temporal fossa ; hence 



i the possibility of being able to identify them even in a skiagram taken from a 

 living subject. \ 



The sphenoidal sinuses are so deeply placed behind the upper half of the 

 piriform aperture of the nose that their outlines cannot be identified in an 

 antero-posterior skiagram. If the sinuses be filled with bismuth before the 

 skiagram is taken, it will be seen that they produce a well-defined and slightly 

 oval black shadow, about the size of a shilling, situated opposite the superior half 

 of the piriform aperture, the superior limit of the shadow reaching just up to the 

 transverse curvilinear line already referred to, while laterally the shadow reaches 

 J cm. medial to the inferior half of the medial margin of the orbit (Logan Turner). 

 In a profile skiagram of the skull the light shadow produced by the sphenoidal 

 sinus is seen immediately inferior to and in front of the characteristic well-defined 

 cup-shaped shadow formed by the concave floor of the hypophyseal fossa. Inferiorly 

 the sinus area is bounded and to some extent overlapped and obliterated by the 

 dense shadow which corresponds from latero-medially to the tuberculum articulare 

 and the horizontal portion of the great wing of the sphenoid, that is to say, to the 



1 floor of the middle fossa of the base of the skull. This dark shadow is continuous, 

 posteriorly, with that which is caused by the dense petrous portion of the temporal 



i bone. Anteriorly is the shadow of the posterior ethmoidal cells (blurred by that 

 produced by the vertical portion of the great wing of the sphenoid), while 

 posteriorly it is limited by the shadow produced by that portion of the body of the 



1 sphenoid ^which lies inferior to the dorsum sellse. 



HYPOPHYSIS CEREBRI. 



The topography of the sella turcica, which lodges the hypophysis cerebri, 

 is of importance now that surgery has succeeded in dealing with certain 

 tumours and enlargements of this organ. The fossa hypophyseos lies im- 

 ; mediately behind the superior part of the sphenoidal sinuses, and, in a median 

 sagittal section of the skull, the anterior half of the fossa is seen to project into 

 jWhat would correspond to the supero-posterior angle of the sinuses. The more 

 the sphenoidal sinuses project backwards, beneath the sella turcica, the thinner 

 is the plate of bone which separates the sinus from that part of the posterior 

 i fossa of the base of the skull which supports the pons. When, on the other 

 ' hand, the sphenoidal sinuses are small and do not extend backwards below the 

 sella turcica, the latter may be difficult to identify. In order to reach the 

 'hypophysis surgeons have abandoned the intra-cranial route, partly on account of 

 the damage produced in the brain, and partly because, when the hypophysis 



