Fig. 14.3 in Chapter 14: The Basicranial and Posterior Cranial Anatomy of the Families of the Toxodontia

Fig. 14.3. Schematic representation of the interpretation of ectotympanic bulla development. Crosssection through the ventral cranium, midline of the petrosal. Stippling indicates (basi)occipital; diagonal lines indicate petrosal; horizontal lines indicate squamosal; solid black indicates ectotympanic. A, ringlike ectotympanic supports tympanum; B, medial and lateral edges of ectotympanic develop; C, medial edge begins to inflate beneath ventral surface of petrosal and lateral moiety begins to expand, forming external auditory meatus; D, ventral inflation proceeds faster than medial edge development, causing appearance of medial recurving; E, ectotympanic bulla covers petrosal, recurved medial edge of ectotympanic lies ventral to, but does not fuse with, petrosal, giving appearance of septum.