Chap. VIII.] THE SKELETON. 157 



two somewhat irregular tri-radiate bones, the vomers (vo.), 

 which send their longest ray backwards and inwards towards 

 the point of the para-sphenoidal dagger. Each vomer bears a 

 little patch of teeth. There are no turbinal bones or distinct 

 cartilages within the nasal chambers. 



(3.) The Auditory Chamber. The anterior part of the ex- 

 occipital, that in front of the foramina for the ninth and 

 tenth nerves may represent epiotic and opisthotic elements. 

 The prootic is well developed as a separate bone, though it too 

 eventually fuses with the ex-occipitals. It sends outwards a 

 shelf (tegmen tympani) over the irregular and ill-defined tym- 

 panic cavity. In the fresh skull there is a ring of cartilage 

 over which the tympanic membrane is stretched. At the 

 bottom of the cavity is the fenestra ovalis (/. 0.), a large hole 

 in the prootic'in the dried skull, but partly filled in with fibrous 

 tissue in the fresh state. A stapes, to which the columella is 

 attached, fits into the fenestra ovalis. 



(4.) The Optic Chamber. The large orbits have the following 

 boundaries : Anterior, nasals above and palatines (pi.} below, 

 the latter bones being slender transverse curved rods. Posterior, 

 prootic above and guard of the para-sphenoid below. External, 

 the pterygoids (pt.), large tri-radiate bones with the longest 

 ray abutting against, and supported by, the maxillae (mx.), and 

 the shortest bending round towards the para-sphenoid. The 

 upper and hinder part of the external boundary is formed by 

 the hammer-like head of the squamosal. Internal, parieto- 

 frontals above, para-sphenoidal blade below, and sphenethmoid 

 anteriorly. 



(5.) The Maxillary fiegion. Both pre-maxillse and maxillae bear 

 teeth. The former are small bones (p.rnx.), with well-marked 

 ascending processes. The maxillae are long, and they too have 

 ascending nasal processes. They are supported by the out- 

 wardly directed palatines (pi.), and the longer limbs of the 

 tri-radiate pterygoids (pt.). A slender quadrato-jugal connects 

 the maxilla with the outer limb of the pterygoid and the handle 

 end of the squamosal. 



(6.) The Mandible. The lower jaw articulates with a cartila- 



