346 



ANATOMY IN A NUTSHELL. 



10. That part of the first frontal convolution which appears on the median 

 side of the hemisphere is the marginal gyrus, or it is that gyrus which arches 

 over the extremity of the fissure of Sylvius. 



11. Occipital gvri are the three principal convolutions of the occipital lobe 

 of the cerebrum, separated by two small transverse sulci, and distinguished as 

 first, second, and third; from above downward, superior, middle, and inferior. 



12. The orbital gyri are upon the under or orbital surface of the frontal 

 Lobe <>!' the cerebrum, which rest upon the orbital plate of the frontal bone. 

 They are three in number, directly continuous with and corresponding to the 

 frontal gyri. The two which are best marked are sometimes called internal 

 and external. 



13. The parietal gyri are four well-marked convolutions upon the superior 



PLATE CLXVI. 



MEDULLA OBLONGATA 



OPTIC THALAMUS 



EPENCEPHALON 



TERMINALS \ OLFACTORY DIVERTICULUM 



CEREBRAL HEMISPHERE 



& 



MID BRAIN FORAMEN OF MONRO 



A Horizontal Section of a Vertebrate Brain. 



and lateral surface of the parietal lobe; and especially two of these distinguished 

 as the ascending parietal or posterior central and the superior parietal, the 

 other two being commonly known as the supramarginal and angular gyrus. 



14. Quadrate, or quadrate gyrus, is a convolution of somewhat square 

 figure appearing on the median surface of the cerebrum between the callosum 

 marginal sulcus in front and the parietooccipital sulcus behind, and continu- 

 ous below with the gyrus fornicatus, also called precuneus. 



L5. Sigmoid gyrus is the somewhat S-shaped fold which curves about the 

 Lateral end of the cruciate fissure and whose surface includes several constant 

 and well-marked "motor areas." 



lii. The temporal gyri, a general name of the temporal convolutions. 



17. Uncinate gyrus is in the median surface of the cerebrum nearly op- 

 posite the gyrus fornicatus. 



Is. Gyri operti ("covered gyrus") is the insula. 



L9. The dentate gyrus is lodged in the hippocampus fissure, and is a long 

 slender roll of gray substance, notched upon its exposed surface. 



