ANATOMY IN A NUTSHELL. 



345 



cealed in the Sylvian fissure, consisting of five or six radiations, convolutions, 

 or the gyri operti ("covered gyrus"). 



Different human brains vary in details of the gyri. and the same brain may 

 differ on its opposite sides. The gyri are best marked when one reaches his 

 highest mental development. 



The principal gyri or convolutions are: (Plate CLXXV-CLXXXIII- 

 CLXXXIV). 



1. Angular gyrus is a short one, arching over the upper extremity of the 

 superior temporal fissure, the hindmost one of the four parietal gyri, separated 

 by a short vertical sulcus from the supra-marginal gyrus. 



2. Annectent gyrus is a small fold wich may connect large or primary con- 

 volutions; applied to several such gyri on the occipital lobe, as those forming 

 the connections of the cuneus or occipital lobule. 



3 Ascending frontal gyrus is the one bounding the fissure of Rolando in 

 front. 



PLATE CLXV. 



SURFACE ECTODERM ^^ 

 NEURAL CREST (DISAPPEARING) 



TJEURAL CREST 

 GANGLION 



POSTERIOR NERve 



SPINAL GANGLION 



SYMPATHETIC GANGLION / ANTERIOR NERVE ROOT 



Showing the Development of the Sympathetic Nerve. 



As ascending parietal is the one bounding the fissure of Rolando behind. 



5. Calossal gyrus is a convolution of the median surface of the cerebrum 

 immedately over the corpus callosum and below the calloso-marginal fissure. 

 It is continuous behind with the gyrus hippocampi, and ends in the gyrus un- 

 cinatus, also called gyrus fornicatus, convolution of the corpus callosum. 



6. Cuneate gyrus is one of the occipital lobe appealing as a wedge-shaped 

 figure on the median aspect of the cerebrum in the fork between the parieto- 

 occipital sulcus and the calcarine sulcus, also called occipital lobule and cuneus. 



7. External orbital gyrus is that part of the orbital surface which lies out- 

 side of the triradiate sulcus. 



8. The frontal gyri, three gyri which compose the superior and lateral 

 surface of the frontal lobe of the cerebrum, all lying in front of the ascending 

 frontal gyrus. They are denned by the superior and inferior frontal sulci, and 

 by the vertical fissure or precental sulcus. 



9. The hippocampal gyrus is the continuation of the gyrus fornicatus 

 where it dips down behind and below the corpus callosum, and continues for- 

 ward to the uncinate gyrus: so-called from its relation to the hippocampus. 



