8o THE CEREBRUM. 



occipital lobes. These two lobes are directly continuous with 

 each other on their inferior surfaces, and are only separated arbi- 

 trarily by an imaginary line drawn from the preoccipital notch 

 to the anterior end of the calcarine fissure. They are only partially 

 separated from the gyrus hippocampi; the ectorhinal sulcus 

 (s. rhinalis) and the anterior part of the collateral fissure lie 

 between the temporal lobe arid the hippocampal gyrus of the 

 limbic lobe; w r hile the inferior surface of the occipital lobe is 

 separated from the gyrus cinguli, of the limbic lobe, by the anterior 

 calcarine fissure. The fissures and sulci of the tentorial area 

 are the following: 



Chorioidal fissure (f. chorioidea) 



Hippocampal fissure (f. hippocampi) 



Ectorhinal sulcus (s. ectorhinalis) 



Collateral fissure (f. collateralis) 



Inferior temporal sulcus (s. temporalis inferior). 



The chorioidal fissure (/. chorioidea) forms a part of the 

 medial boundary of the tentorial area (Figs. 26 and 28). At the 

 surface it appears to be identical with the hippocampal fissure; 

 but, upon looking deeper, the two are found to be separated by 

 the fascia dentata and the crus of the fornix. This fissure is 

 separated from the inferior horn of the lateral ventricle, only by a 

 layer of epithelium, 'derived from the roof plate of the telencepha- 

 lon. It contains the chorioid plexus of the inferior horn. 



Hippocampal Fissure. (F. hippocampi, Fig. 28). Along the 

 medial and concave border of the hippocampal gyrus is the cres- 

 centic fissure known as the hippocampal fissure. The fissure 

 in front is closed by the uncus. It extends backward to the 

 splenium of the corpus callosum where, in the adult, it is con- 

 tinuous with the furrow behind and above the corpus callosum, 

 called the callosal sulcus. The hippocampal is a true fissure as 

 it indents the whole ventricular wall ; the long ventricular eminence 

 produced by it is the hippocampus seen in the inferior horn of 

 the lateral ventricle (see medial surface of the cerebral hemisphere). 



Ectorhinal Sulcus. (Incisura temporalis, Figs. 26 and 29). 

 Midway between the temporal pole and the hook-point of the 

 hippocampal gyrus is a slight notch, called the ectorhinal sulcus, 



