THE EAK. 



391 



IS, 



la rarer 



Fi.u-. 243. 



The interstapedial (Fig'-s. 12 a, 243 c) is eartilag-iiious ; it is 

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

 against ^q fenestra ovalh. The inner surface of the interstapedial 

 however, distinctly 

 r than the opening 

 of \)a& fenestra ovalis, con- 

 sequently it does not fit 

 in accurately, but is at- 

 tached to the border of 

 the ojjening' by means of 

 connective - tissue ; the 

 margins of the fenestra 

 oralis 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 i.s 

 attached. 



B, The labyrinth onin- 

 teriial ear is contained in a 

 capsule formed of bone 

 and cartilage. 



Tlie ooluiuella ; after Retzius. Magnitied eight times. 



A. Seen from above. 



B. Seen from behind. 



'(' Extrastapedial (Parker). Outer cartilaginous portion 

 attached to middle of tympanic membrane (Retzius). 



a" Attachment of extrastapedial to inediostaiDedial. 



a"' Suprastapedial( Parker). Portion embedded in mucous 

 membrane (Retziua^ 



ii^. _ Mediostapedial ^-aiiet). ' Bony part (Retzius). 



&'" • Process of mediostapedial. 



(■ Interstapedial (Parker). Inner cartilaginous piece 

 (Retzius). 



m Insertion of small muscle. _^ —- ■ 



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 the 

 membranou.s ear. 



Four surfaces can be distinguished : a supero-external, 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 processus squaniosns inootici. 

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

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



