ABSTRACT
The walls and roof of the fourth ventricle are formed in their rostral part by the superior cerebellar peduncles and the superior medullary velum, and in their caudal part, interrupted by the median aperture, by the ventricular ependyma and the pia mater of the tela choroidea. The floor of the fourth ventricle, or rhomboid fossa, is divided into three areas. The superior area, limited laterally by the superior cerebellar peduncles and caudally by an arbitrary line through the rostral ends of both superior foveae, is continuous rostrally with the cerebral aqueduct’s wall. The intermediate area is characterized by the striae medullares. The inferior area, showing mainly the hypoglossal and vagal triangles, is continuous below with the wall of the central medullary canal (Williams et al., 1989). The floor is divided vertically by a median sulcus that seems to have been described by Herophilus, who coined the term calamus scriptorius (pen nib). The question is to know what he exactly meant with this term (calamus), which is known to be at the root of about 45 terms in different languages (Delaveau, 1995).
