Commentary Inf XIV 76-84

The little stream that the travelers now see is the second (and last) body of water that moves across their usual circular path and downward (see [Inf VII 100-108], where the descent from the fourth to the fifth Circle is made alongside a little stream that seems -- but we never receive 'official' confirmation -- to connect Acheron to Styx). All other gatherings of water have been circles that they had eventually to cross in order to descend. We will soon be able to understand (vv. 115-117) that this particular stream contains waters from Phlegethon that will eventually fall into the frozen Cocytus (heard tumbling down to the eighth Circle at [Inf XVI 1-2]). Dante and Virgil apparently do not happen to see the stream that connects Styx to Phlegethon because, as Virgil suggests ([Inf XIV 128-129]), their path does not include full circles in a given zone (e.g., their passage along Phlegethon, which covers exactly a semicircle, in Inf. XII). For a lengthy and helpful review of the 'hydraulic system' of hell -- which nonetheless remains difficult to understand -- see DDP Singleton.Inf.XIV.121-138.

The Bulicame is a hot spring near Viterbo from which prostitutes, perhaps not allowed to frequent the public baths, made conduits from the source to service their own dwellings.

The passage to the next and deeper zone of the burning sand now lies right before them (it is a necessary expedient, we want to remember, to get Dante across the burning sand); before they can follow it, Virgil will take up the subject of the waters of hell.