When the hounds of spring are on winter’s traces,"The mother of months" is of course Artemis and refers to her role as goddess of the moon. In the first line of the play the chief huntsman addresses her as "Maiden, and mistress of the months and stars." This doesn't seem to be a classical epithet of Artemis or Diana. After a quick search the closest classical parallel I can find is Pseudo-Vergil, Culex 284: menstrua virgo. Others have pointed out that Swinburne may have borrowed the phrase from Shelley, who describes the moon as "the mother of the months" in Revolt of Islam IV.1.7 and Prometheus Bound IV.207.
The mother of months in meadow or plain
Fills the shadows and windy places
With lisp of leaves and ripple of rain;
And the brown bright nightingale amorous
Is half assuaged for Itylus,
For the Thracian ships and the foreign faces.
The tongueless vigil, and all the pain.
Come with bows bent and with emptying of quivers,
Maiden most perfect, lady of light,
With a noise of winds and many rivers,
With a clamour of waters, and with might;
Bind on thy sandals, O thou most fleet,
Over the splendour and speed of thy feet;
For the faint east quickens, the wan west shivers,
Round the feet of the day and the feet of the night.
Where shall we find her, how shall we sing to her,
Fold our hands round her knees, and cling?
O that man’s heart were as fire and could spring to her,
Fire, or the strength of the streams that spring!
For the stars and the winds are unto her
As raiment, as songs of the harp-player;
For the risen stars and the fallen cling to her,
And the southwest-wind and the west-wind sing.
For winter’s rains and ruins are over,
And all the season of snows and sins;
The days dividing lover and lover,
The light that loses, the night that wins;
And time remember’d is grief forgotten,
And frosts are slain and flowers begotten,
And in green underwood and cover
Blossom by blossom the Spring begins.
The full streams feed on flower of rushes,
Ripe grasses trammel a travelling foot,
The faint fresh flame of the young year flushes
From leaf to flower and flower to fruit;
And fruit and leaf are as gold and fire,
And the oat is heard above the lyre,
And the hoofed heel of a satyr crushes
The chestnut-husk at the chestnut-root.
And Pan by noon and Bacchus by night,
Fleeter of foot than the fleet-foot kid,
Follows with a dancing and fills with delight
The Mænad and the Bassarid;
And soft as lips that laugh and hide
The laughing leaves of the trees divide,
And screen from seeing and leave in sight
The god pursuing, the maiden hid.
The ivy falls with the Bacchanal’s hair
Over her eyebrows hiding her eyes;
The wild vine slipping down leaves bare
Her bright breast shortening into sighs;
The wild vine slips with the weight of its leaves,
But the berried ivy catches and cleaves
To the limbs that glitter, the feet that scare
The wolf that follows, the fawn that flies.
Hat tip: Alan Knell.