The largest of the subarachnoid cisterns between the cerebellum and the medulla oblongata; it is divided into a posterior cerebellomedullary cistern located between the cerebellum and the posterior surface of the medulla (also called cisterna magna), and a lateral cerebellomedullary cistern located between the cerebellum and the lateral aspect of the medulla. [ http://www.drugs.com/dict/cerebellomedullary-cistern.html ]