Thick sagittal section through the hindbrain of a 4 months’ human embryo. The cavity of the fourth ventricle (1) is shown, extending forwards to the hinder end of the cerebral aqueduct (3). In the roof of the ventricle is seen the cerebellum, which at this stage is beginning to develop its fissures. The posterior or lower part of the roof is formed by the inferior medullary velum, and here the lining membrane of the ventricle is invaginated by vascular tufts to form the choroid plexus (2). This section shows rather well the essential nature of the choroid plexuses of the brain – invaginations of vascular pia mater covered on their ventricular aspect by the ventricular lining (ependyma).  In the section are also to be seen the cisterna magna (5) and the tectum of the mid-brain (4). The photograph is at magnification of X 14.

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