The vertebral column develops during early embryogenesis.  It is formed from a periodic pattern of somites along the anterior- posterior axis of an organism.  These somites are rounded structures formed after compaction and segmentation of mesenchymal cells. There is an intricate pattern of gene activity and protein expression which appears to be involved in the rounding process. However, here we consider the physical aspects of the mechanism. Current theory is that increased cell-cell adhesion induces minimization of the tissue surface tension, yielding rounded tissue. We investigate this behaviour using a viscous liquid model of tissue dynamics.  Given the relatively brief time in which somite formation occurs, and the high bulk viscosities of tissues, the basic model is unconvincing. We propose a simple chemotactic mechanism to extend the model.  This new model successfully produces rounding within the timeframe found in vivo.