The highly-regarded striker made his Spurs debut earlier this season when he appeared off the bench in the club's Europa League clash at home to Russian side Anzhi Makhachkala in December.
Coulthirst, capped at Under-19 level for England, is available to make his O's debut in Saturday's FA Cup third-round clash at Yeovil.
Ness, 22, has yet to feature for the Potters this campaign and heads to Brisbane Road in search of first-team football.
Along with Coulthirst, the former Rangers man is available to face Yeovil this weekend.
- Sports & Recreation
- Anzhi Makhachkala