FIG. 17 in The Serrialis Bone, Interparietals, "X" Elements, Entotympanics, And The Composition Of The Notoungulate Caudal Cranium

FIG. 17. Protypotherium sp. MLP 12-2780, virtual coronal sections through caudal cranium, apparent right side: rostral (A), middle (B), and caudal (C) portions of middle ear (A and C rev.). All to scale in C. For approximate locations of sectioning planes, see fig. 16B. Although this matrix-embedded specimen is in good condition overall except for damage to thecal walls, CT resolution is relatively poor and fine details cannot be discriminated. Note well developed medial paratympanic cavity in A and B. In B, arrow identifies approximate position of suture between squamosally derived theca and caudal crus of ectotympanic, not evident in this section but clearly present in others, confirming that squamosal contributes the most to epitympanic sinus enclosure. In C, caudal part of highly trabeculated epitympanic sinus extends deep into retrotympanic process (asterisk). Suture between supraoccipital and overplated interparietal is obvious.