FIG. 8. A, Caluromys derbianus AMNH M-18910 in Transverse Canal Foramen And Pericarotid Venous Network In Metatheria And Other Mammals

FIG. 8. A, Caluromys derbianus AMNH M-18910 (Didelphidae, Didelphimorphia), adult caudal cranium in oblique caudoventral view. B, Caluromys sp. AMNH M-184599 (Didelphidae, Didelphimorphia), adult caudal cranium in endocranial view. Although transverse canal foramen is usually scored as completely absent in the short-tailed opossum group, in A a tiny dimple (single asterisk) lateral to exocranial opening of right carotid canal may represent vestige of vein's trackway, assuming it differentiated but did not persist. Equivalent opening is not seen on left side or in B. There is no swelling or eminence for transverse canals on endocranial floor, consistent with rostral branch tubes not being present. Endocranial carotid grooves contain only one aperture, for internal carotid neurovascular bundle, indicating caudal branch of transverse canal vein is also absent in this taxon. Note well marked foramina for craniopharyngeal (feature 1) and notochord (feature 2) canals.