We propose a volume radiofrequency coil for MRI that provides a lateral access to its inner volume. This coil, called «opencage», is designed by revisiting birdcage coils as metamaterial transmission line with broken periodicity. An opencage dedicated for imaging at 7T of the head of small rodents is developed. The design of this opencage is optimized using numerical simulation. Finally in-vivo preclinical imaging of the head of a mouse is presented. We show that the opencage coil efficiency is similar, especially in terms of field homogeneity and SNR as a conventional 8-legs birdcage coil.