Becker, M. B., Zuelch, A., Bosse, A., & Gruss, P. (2001). Irx 1 and Irx 2 expression during early lung development. Mechanisms of Development, 106, 155-158. Retrieved from http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T9H-43J0R4T-K-1&_cdi=5115&_user=38661&_pii=S0925477301004129&_origin=search&_coverDate=08%2F31%2F2001&_sk=998939998&view=c&wchp=dGLzVzb-zSkWA&md5=07b2b293c4eee5d322e00cdf842ef2c6&ie=/sdarticle.pdf.