FIG. 38. Sipalocyon gracilis AMNH VP-9254 (Hathliacynidae, Sparassodonta), adult specimen, endocast reconstruction showing osteological features associated with pericarotid venous network and related vasculature (data source, table 2; color key, fig. 4). Views: A, ventral; B, same, with transverse basisphenoid sinus superimposed; C, oblique right lateral; D, closeup of endocranial surface of mesocranial region; and E, caudoventral surface, intact caudal cranium showing extracranial continuation of ventral petrosal sinus. In A–C, rostral portion of transverse basicranial sinus lacks identifiable intramural connections with carotid canals or cavernous sinus. Feature 1, identified by Archer (1976) as a possible transverse canal in Sipalocyon, is more likely a channel for nerve of pterygoid canal. Feature 2 is a sulcus of unknown function, unrelated to either nerve of pterygoid canal or typical transverse canal. Feature 3, small channel within basisphenoid sinus tissue, presumably venous, passes between bilateral carotid canals (double-headed arrow in D) caudal to hypophyseal fossa. Arrangement is different from that of CBTC of investigated marsupials. Feature 4, another small canaliculus, either interstitial or remnant of notochord canal, connects feature 3 with rest of sinus. Key: cc, carotid canal; cchc, caudal condylohypoglossal canal; ctbs, caudal portion of