[Illustration: FIGS. 16-17. Transverse sections through otic region: 16) at level of prootic foramen; 17) at level of anterior acoustic foramen. Abbreviations: _angspl._, angulosplenial; _ant. acus. f._, anterior acoustic foramen; _cr. par._, crista parotica; _fpar._, frontoparietal; _max._, maxillary; _Mc. c._, Meckel's cartilage; _ot. cap._, otic capsule; _pasph._, parasphenoid; _pro._, prootic; _psdbas. proc._, pseudobasal process; _pter._, pterygoid; _pter. proc._, pterygoid process; _qj._, quadratojugal; _sq._, squamosal; _tect. syn._, tectum synoticum; _tymp. r._, tympanic ring.] [Illustration: FIGS. 18-19. Transverse sections through otic capsule: 18) at level of posterior acoustic foramen; 19) at level of jugular foramen. Abbreviations: _angspl._, angulosplenial; _corn. prin._, cornu principalis; _cr. par._, crista parotica; _exocc._, exoccipital; _fpar._, frontoparietal; _jug. f._, jugular foramen; _max._, maxillary; _Mc. c._, Meckel's cartilage; _ot. cap._, otic capsule; _p. ext. pl._, pars externa plectri; _p. int. pl._, pars interna plectri; _p. med. pl._, pars media plectri; _pasph._, parasphenoid; _post. acus. f._, posterior acoustic foramen; _postlat. cr. par._, posterolateral edge of crista parotica; _pro._, prootic; _pter._, pterygoid; _pter. proc._, pterygoid process; _quad. proc._, quadrate process; _qj._ quadratojugal; _sq._, squamosal; _tect. syn._, tectum synoticum; _tymp. r._, tympanic ring.] At the level of the anterior acoustic foramen the cornu principalis of the hyale (_corn. prin._) appears as a lateral ledge at the ventrolateral corner of the otic capsule (Fig. 20a-b). The cornu principalis diverges from the ledge at the level of the abbreviated bridge between the anterior and posterior acoustic foramina. In posterior sections the cornu lies medial to the squamosal-pterygoid process-pterygoid complex (Fig. 18). The posterior terminus of the cornu lies at a level with that of the posterior acoustic foramen. The pars externa plectri (_p. ext. pl._, Fig. 20a-b) is cartilaginous and first appears dorsal to the ventral arm of the squamosal in association with the tympanic membrane. The pars externa plectri expands dorsomedially and is fused briefly to the crista parotica by the pars ascendens plectri (_p. asc. pl._, Fig. 20b). The pars interna plectri (_p. int. pl._, Fig. 20b-f) is cartilaginous and appears medial to the pars media plectri and the ventrolateral ledge of the otic capsule at the level of the anterior acoustic foramen. The pars media plectri (_p. med. pl._, Fig. 20b-f), a cartilage and bone element, appears proximally at the dorsolateral edge of the otic capsule and distally, ventral to the squamosal at a level between the anterior and posterior acoustic foramina. At the level of the posterior acoustic foramina the pars media plectri is bony, greatly expanded in size, and joined to the pars interna plectri medially.