QO THE CEREBRUM. 



and the anterior calcarine fissure is separated from the posterior 

 calcarine by the gyrus cuneo-lingualis (Cunningham). The 

 anterior calcarine fissure indents the medial wall of the posterior 

 horn of the lateral ventricle, producing the calcar avis. 



Hippocampal Fissure (Figs. 26 and 28). A crescentic fissure, 

 convex downward begins under the splenium of the corpus cal- 

 losum in continuity with the callosal sulcus, and winds forward 

 beneath the thalamus to within an inch of the temporal pole, 

 where it is closed by the uncus. It is the hippocampal fissure. 

 On the surface of the temporal lobe this fissure appears to be 

 identical with the temporal extension of the chorioidal fissure; but, 

 deeply, it lies posterior to that fissure and is separated from it 

 by the fascia dentata. The hippocampal fissure produces a long 

 ridge in the inferior horn of the lateral ventricle, called the hip- 

 pocampus. 



The chorioidal fissure (Figs. 28 and 39) describes about 

 two-thirds of a circumference along the concavity of the fornix. 

 It extends from the foramen interventriculare backward over 

 the thalamus; and then downward and forward along the hip- 

 pocampal fissure, but separated from it by the dentate fascia. The 

 chorioidal fissure is a complete one, involving the whole hemisphere 

 wall. A single layer of epithelium separates it from the lateral 

 ventricle. The pia mater, dipping into it, forms the chorioid 

 plexus of that ventricle. The fissure is peculiar in the fact that 

 between the inter-brain and the fornix there is a transverse slit 

 by means of which it is continuous with the same fissure on the 

 opposite side. In this antero-superior part, which is in direct 

 continuity with the transverse fissure of the cerebrum, is the border 

 of the chorioid tela of the third ventricle. 



Collateral Fissure. The collateral is a long fissure (Figs. 

 26 and 28). It reaches from near the occipital almost to the 

 temporal pole. It is situated below and parallel with the cal- 

 carine and hippocampal fissures, being separated from the former 

 by the lingual gyrus and from the latter by the hippocampal gyrus. 

 The gyrus fusiformis lies below and external to this fissure. Ante- 

 rior to the collateral fissure, there is a small sulcus between the 

 gyrus hippocampi and the temporal pole, called the ectorhinal 



