884 MR. R. W. PALMER ON THE 



of the glenoid fossa, where the squamosal meets the alisphenoid, 

 there is a narrow ridge which both bones help to form, and which 

 runs parallel to the middle line to separate the glenoid and 

 tympanic cavities. Where this ridge meets the post-glenoid 

 process there is a depression which may represent a venous 

 foramen (text-fig. 153,/., p. 881). 



Seen from the inside the periotic is quite an extensive bone. 

 The double openings of the internal auditoiy meatus and of the 

 aqueductus Fallopii are seen in the centre of the lower triangular 

 part. Above this, the floccular fossa {f.fo.) is excavated, and 

 from this region the large mastoid portion inclines backwards. 

 The mastoid part, as mentioned, is exposed on the outside of the 

 skull only as a small island between the exoccipital and the 

 squamosal, forming the lambdoid crest for about 1'5 cms. Through 

 its suture with the exoccipital runs the small mastoid foramen 

 (ni.f.). The inferior surface of the petrosal portion is seen as a 

 subovate mass inclined steeply outwards and jammed in between 

 the basioccipital and squamosal. It separates the median and 

 posterior lacerate foramina. Posteriorly it is pierced by the 

 fenestras rotunda and ovalis. 



The tympanic is preserved on the left side. It is partly 

 anchylosed to the squamosal, but not to the periotic. It consists 

 of a small, very thick, uninflated bulla which does not meet the 

 basioccipital, but projects freely under the petrosal. A cylin- 

 drical hollow on the bone represents the attachment of the 

 tympano-hyal (t.hi/.), and on the right side the position of the 

 stylomastoid foramen (stm.f.) is seen to be immediately behind 

 this. The rest of the bone forms an irregular mass below the 

 meatus and presents no points of interest. 



The cdisp>henoids ai'e firmly fused with the basisphenoid, and 

 the three bones must be taken together. The basisphenoidal part 

 is very elongated — behind, it is wide and notched by the mediari 

 lacerate foramina. In front, it narrows very considerably, and 

 at the junction with the alisphenoidal part the vertical pterygoid 

 wings arise. The alisphenoidal part is a hatchet- or L-shaped 

 bone, having a narrow limb confined to the base of the skull 

 between the squamosal and the basisphenoid and a square limb 

 in front of this, forming part of the side wall of the skull and 

 meeting the parietal above and the frontal in front. The long 

 limb is deeply grooved for the Eustachian tube, and in its middle 

 is perforated by the foramen ovale (f.ov.). Anteriorly, below 

 the pteiygoid flange, the bone is tunnelled by a canal which 

 represents the united sphenoidal fissure and foi-amen rotundum 

 (III.- VI.). A couple of venous foramina (v/,) appear externally 

 on the alisphenoid. These were traversed by the vessels Avhich 

 united inside the skull to foi'm the large vein already mentioned 

 as running into the transverse sinus. On its upper surface the 

 alisphenoid is very deeply grooved to shelter the cranial nerves 

 lying on it. These grooves are better seen from the cast. They 

 will be mentioned later. In section, the basisphenoid is seen to 



