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\section{Methodology}
To search for more bones, we visually inspect regions (|$l$|\textless 30$^{\circ}$, |$b$|\textless 1$^{\circ}$) where arms are predicted to
lie lie, in $l,b,v$ space, according to our current understanding of the Milky Way's
structure; structure. To carry out our search, we began by calculating the expected ($l,b,v$) paths of
the Galactic arms
are calculated using a log-spiral approximation as described in recent literature \cite{Dame_2011,Vallee_2008}, and
placed on the Sky assuming a an assumed 25 pc height above the plane for the Sun \citep[see][and references therein]{Goodman_2014}. The predicted positions of the Galactic arms (Scutum-Centaurus, Carina-Sagittarius, Norma-Cygnus, and Perseus)
are overlaid were overlain on
three-color Spitzer
GLIMPSE GLIMPSE/MIPSGAL \citep{Benjamin_2003,Churchwell_2009} images in World Wide Telescope (WWT)---a tool that facilitates easy visualization of several layers of data at scales from the full sky down to the highest-resolution details.
As part of our initial criteria, Panning along the full Spitzer/MIPSGAL Survey in WWT, we
search searched for
long, largely continuous, filamentary mid-infrared extinction
features that are features, near and roughly parallel to the Galactic
mid-plane. mid-plane, where all of the overlain arm traces lie. This initial inspection yielded about fifteen
Bone initial bone candidates (a video showing how this search worked in WWT is available \href{http://tinyurl.com/morenessies}{on YouTube}, and the original WWT Tour, of which the video shows a capture, is available at the \href{http://dx.doi.org/10.7910/DVN/29934}{Bones of the Milky Way Dataverse}).
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. The filament must have similar line-of-sight velocities along its length. Moreover, 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 these filaments, we employ 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 thermal emission lines trace dense molecular gas ($\approx10^{4}\textrm{ cm}^{-3}$) 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 ($\approx10^{2}\textrm{ cm}^{-3}$) surrounding these bones using high resolution $^{13}\rm{CO}$ data from the GRS and ThrUMMS survey.
