THE E.UI. 



391 



Fig. 243. 



The interstapedial (Figs. 12 a, 243 c) is cartilaginous; it is 

 thick with a sharply cut-off, slightly concave end, which is placed 

 against the fettesfra ozali*. The inner surface of the interstapedial 

 is, however, distinctly 

 larger than the opening 

 of thefenesfra ovalis, con- 

 sequently it does not fit 

 in accurately, but is at- 

 tached to the border of 

 the opening by means of 

 connective - tissue ; the 

 margins of the feneslra 

 ovalis are hollowed (Fig. 

 245 II) so as to form a 

 fossa fenestrae ovalis, and 

 it is really to the margin 

 of this fossa that the 

 connective-tissue capsule 

 of the interstapedial is 

 attached. 



The coluruella ; after Retzius. Magnified eight times. 



A. Seen from above. 



B. Seen from behind. 



Extrastapedial (Parker). Outer cartilaginous portion 

 attached to middle of tymjxmic membrane (Retains). 



Attachment of extrastapedial to mediostapediaL 



Suprastapedial ( Parker). Portion embedded in mucous 

 membrane (Retzius). 



Mediostapedial (Parker). Bony part (Retzius). 



Process of mediostapedial. 



Interstapedial (Parker). Inner cartilaginous jiiw.- 

 (Retzius). 



Insertion of small muscle. 



B. The labyrinth or in- 

 ternal ear is contained in a 

 capsule formed of bone 

 and cartilage. 



a. The capsule of the labyrinth (Fig. 244) is formed of two 

 bones, the prootic and the exoccipital (according to Hasse this 

 includes the opisthotic). which are united by cartilage belonging to 

 the primordial-cranium. The fronto-parietal, squamosal, and para- 

 sphenoid take only an indirect part in its formation. 



On the whole the anterior half of the capsule is formed by the 

 prootic, and the hinder half by the exoccipital ; the cavity has its 

 long axis directed from within and above, downwards and outward ; 

 the cavity is comparatively large and rounded, and contains tin- 

 membranous ear. 



Four surfaces can be distinguished : a supero-exterual, an interno- 

 inferior, an anterior, and a posterior (Retzius). 



(i) The supero-external surface is divided into two parts by a 

 strong, transverse, bony ridge, the processii* squainoxiix proofki. 

 The upper half is concave, is directed upwards and outwards, and 

 is formed by the prootic ; it is separated from the anterior surface 



