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\subsection{Probing Velocity Structure}  For features that appear associated with spiral arms on the 2-D plane of the sky, radial velocity data is needed to establish whether 3-D association with a spiral feature is likely. Any good bone candidate must have similar line-of-sight velocities along its full length, and more importantly, the measured radial velocities should be very close to those predicted by the Milky Way's rotation curve for arms at a known distance. To probe the velocity structure of the initial bone candidates identified in WWT, we employed radial velocity data from five separate radio surveys: HOPS \citep{Purcell_2012,Walsh_2011}, MALT90 \citep{Foster_2011,Jackson_2013}, BGPS spectral-line follow-up \cite{Schlingman_2011,Shirley_2013,Ellsworth_Bowers_2013}, GRS \citep{Jackson_2006} and ThrUMMS \cite{Barnes_2011}. The HOPS, MALT90, and BGPS surveys are all geared towards probing dense regions hosting the early stages of high mass star formation. We utilize $\textrm{NH}_3$ emission from HOPS, $\mathrm{N_2H^{+}}$ from MALT90, and $\textrm{HCO}^{+}$ from BGPS. All three of these lines trace dense molecular gas ($\sim 10^{4}\textrm{ cm}^{-3}$), and are often found in dense, cool clouds with temperatures less than 100 K \citep{Purcell_2012,Shirley_2013}. As infrared dark clouds tend to harbor cool, high density clumps of gas which fuel the formation of massive stars, all three of these data sets contain spectra for hundreds of regions within the longitude range of the potential Galactic bones. To complement these high density gas tracers, we probe the puffier envelopes ($\sim 10^{2}\textrm{ cm}^{-3}$) surrounding these bones using high resolution $^{13}\rm{CO}$ data from the GRS and ThrUMMS survey.   We investigate the velocity structure of our filaments in two ways: first, whenever possible, we establish the velocity coherence contiguity  of our candidates by performing a slice extraction along each filamentary extinction feature in \href{http://www.glueviz.org/en/stable/index.html}{Glue}, a visualization tool that facilitates the linking of data sets. We link spectral \textit{p-p-v} cubes from the GRS and ThrUMMS survey with GLIMPSE-Spitzer mid-infrared images and obtain velocity as a function of position along a path that traces the entire extinction feature. The results of the slice extraction along the path of one of our strongest bone candidates is shown in figure \ref{fig:filament5_slice}. We are able to establish velocity coherence for all candidates lying within the coverage range of the GRS survey ($ 18^\circ < l < 56^\circ$) and the ThrUMMS survey ($300^\circ < l < 358^\circ$). We also confirm that this GRS or ThrUMMS-determined velocity agrees with the velocity of dense gas tracers to within 5 km/s. Next, we ensure that the candidates are contiguous in velocity space as traced mainly by high-density emission from the HOPS, MALT90, and BGPS surveys. In cases where HOPS, MALT90, and BGPS catalog data are not available along the extinction feature, we also extract spectra from GRS and MALT90 \textit{p-p-v} cubes using the spectrum extractor tool in Glue. We once again link spectral \textit{p-p-v} cubes from the GRS survey with GLIMPSE-Spitzer mid-infrared images and use the spectrum-extractor tool to obtain velocities along different regions of the extinction feature; a demonstration of the procedure used to extract velocities in Glue is shown in the appendix. Since CO traces lower density gas ($\sim 10^2 \textrm{ cm}^{-3}$) and $\mathrm{N_2H+}$, $\textrm{HCO}^+$, and $\textrm{NH}_3$ trace high density gas ($\sim 10^4 \textrm{ cm}^{-3}$), the dense gas sources provide much stronger evidence for the velocity of cold, dense, filamentary IRDCs. However, where dense gas sources are not available, the complete and unbiased high resolution GRS survey, although less desirable, allows us to roughly gauge the velocity along entire lengths of filaments.