The single heavenly dog that is described here is of no mean interest. The passage proves the individual character of each of the two dogs of Yama; they cannot be a vague pair of heavenly dogs, but must be based each upon some definite phenomenon in the heavens.
Yet another text, Hiranyakeçin's book of house-rites, locates the dogs of Yama, describing them in unmistakable language, in heaven: "The brood of Saram[=a], dark beneath and brown, run, looking down upon the sea." (ii. 7. 2.)
There are not many things in heaven that can be represented as a pair, coursing across the sky, looking down upon the sea, and having other related properties. My readers will make a shrewd guess, but I prefer to let the texts themselves unfold the transparent mystery. The Veda of the _Katha_ school (xxxvii. 14) says: "These two dogs of Yama, verily, are day and night," and the Br[=a]hmana of the _K[=a]ush[=i]takins_ (ii. 9) argues in Talmudic strain: "At eve, when the sun has gone down, before darkness has set in, one should sacrifice the _agnihotra_-sacrifice; in the morning before sunrise, when darkness is dispelled, at that time, one should sacrifice the _agnihotra_-sacrifice; at that time the gods arrive. Therefore (the two dogs of Yama) Çy[=a]ma and Çabala (the dark and the spotted) tear to pieces the _agnihotra_ of him that sacrifices otherwise. Çabala is the day; Çy[=a]ma is the night. He who sacrifices in the night, his _agnihotra_ Çy[=a]ma tears asunder; he who sacrifices in broad daylight, his _agnihotra_ Çabala tears asunder." Even more drily the two dogs of Yama are correlated with the time-markers of heaven in a passage of the _T[=a]ittir[=i]ya-Veda_ (v. 7. 19); here sundry parts of the sacrificial horse are assigned to four cosmic phenomena in the following order: 1. Sun and moon. 2. Çy[=a]ma and Çabala (the two dogs of Yama). 3. Dawn. 4. Evening twilight. So that the dogs of Yama are sandwiched in between sun and moon on the one side, dawn and evening twilight on the other. Obviously they are here, either as a special designation of day and night, or their physical equivalents, sun and moon. And now the _Çatapatha-Br[=a]hmana_ says explicitly: "The moon verily is the divine dog; he looks down upon the cattle of the sacrificer." And again a passage in the Kashmir version of the _Atharva-Veda_ says: "The four-eyed dog (the moon) surveys by night the sphere of the night."