Sympathetic neurons of SCG (Superior Cervical Ganglia) send axonal projections either along the external carotid arteries to innervate the salivary glands, or along the internal carotid arteries to the lacrimal and pineal glands, the eye, blood vessels and skin of the head, and the mucosa of the oral and nasal cavities. Previous studies using Wnt1Cre and R26R have defined the neural crest and mesodermal origins of vascular smooth muscle in the heart outflow tract and great vessels, although not specifically of the segments that are relevant for the projections of the SCG neurons. The third pharyngeal arch arteries are lined by neural crest-derived smooth muscle, and consequently, their derivatives, including the entirety of the external carotid arteries and only the base of the internal carotid arteries, also have a neural crest origin. In contrast, the dorsal aortae are lined by smooth muscle that is mesodermal in origin, and as a result, the internal carotid arteries from just above their origination from the common carotid arteries have a mesoderm-derived smooth muscle layer. To address the possibility that guidance cues for SCG neurons are selectively expressed by the external carotid vs. the internal carotid arteries, we isolated these segments of the vasculature from mouse embryos at E13.5 and extracted RNA to screen microarrays for differentially expressed genes.