  The central molecular zone (CMZ) hosts some of the most massive and dense
molecular clouds and star clusters in the Galaxy, offering an important window
into star formation under extreme conditions. Star formation in this extreme
environment may be closely linked to the 3-D distribution and orbital dynamics
of the gas. Here I discuss how our new, accurate description of the $\{l,b,v\}$
structure of the CMZ is helping to constrain its 3-D geometry. I also present
the discovery of a highly-regular, corrugated velocity field located just
upstream from the dust ridge molecular clouds (which include G0.253+0.016 and
Sgr B2). The extremes in this velocity field correlate with a series of massive
($\sim10^{4}$ M$_{\odot}$) cloud condensations. The corrugation wavelength
($\sim23$ pc) and cloud separation ($\sim8$ pc) closely agree with the
predicted Toomre ($\sim17$ pc) and Jeans ($\sim6$ pc) lengths, respectively. I
conclude that gravitational instabilities are driving the formation of
molecular clouds within the Galactic Centre gas stream. Furthermore, I suggest
that these seeds are the historical analogues of the dust ridge molecular
clouds - possible progenitors of some of the most massive and dense molecular
clouds in the Galaxy. If our current best understanding for the 3-D geometry of
this system is confirmed, these clouds may pinpoint the beginning of an
evolutionary sequence that can be followed, in time, from cloud condensation to
star formation.

Astrophysics of Galaxies