deletions | additions       diff --git a/CO_velocities.tex b/CO_velocities.tex  index e9d6d68..70cdc1a 100644  --- a/CO_velocities.tex  +++ b/CO_velocities.tex 
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\subsubsection{CO Velocities}  \label{CO}  CO observations trace gas with mean density around 100 \cc. cm$^{-3}$.  CO emission associated with the Scutum-Centaurus Arm of the Milky Way is shown in Figure \ref{fig:COarm}, which presents a plane-of-the-sky map integrated over $-50 \cc. cm$^{-3}$.  Thus, the plane-of-the-sky coincidence of the line-of-sight-velocity-selected ``Scutum-Centaurus" CO emission and the mid-IR extinction suggests that the Nessie IRDC may be a kind of ``spine" or ``bone" of this section of the Scutum-Centaurus Arm. But, the spatial resolution of the CO map is too low ($8'$), and the 20 km\ s$^{-1}$ velocity range associated with the Arm in CO is too broad to decide based on this evidence alone whether Nessie is a well-centered ``spine" or just a long skinny feature associated with, but potentially significantly inclined to, the Scutum-Centaurus Arm.