HYLOBATES HOOLOCK, THE GIBBON 41- 



the cerebellum. The petroso-ventricular surface of the cerelx'lhim presents a 

 fairly large flocculus occupying the cerebello-pontile angle. The mesial por- 

 tion of this surface is in relation with the roof of the fourth ventricle. 



FIG. ig6. RIGHT LATERAL SURFACE OF BRAIN, HYLOBATES HOOLOCK. 



[Actual Length 73 mm.] 



Key to Diagram, obl., Oblongata; sulc. occip., Sulcus Occipitalis; sulc. occip. lat., Sulcus Occipitalis 

 Lateralis; cerebl., Cerebellum; sulc. precnt. inf., Sulcus Precentralis Inferior; sulc. ret. sup., Sulcus 

 Retrocentralis Superior; sulc. simiarum, Sulcus Siraiarum; s. ret. i.. Sulcus Retrocentralis Inferior. 



THE BRAIN STEM 



In the brain stem, the markings on the several surfaces in gibbon are 

 more precise than in the lower primates, and about equally as distinct as 

 they arc in the baboon and macacus. 



The Oblongata. The oblongata upon its ventral surface presents a 

 well-defined ventromedian sulcus, which is flanktxl upon either side by 

 t\\o fairly prominent pyramidal elevations. Lateral to the pyramid and 

 separated from it by a pre-olivary sulcus is a well-defined olivary eminence 

 whose contour and proportions are somewhat more marked than in the other 

 intermediate primates. The lateral surface shows the gradual gathering of 

 the ascending spinocerebellar fibers until this collection forms the restiform 

 body at the lower border of the pons Varolii. In the lower portion of the 

 lateral surface there is a slight protuberance which marks the surface relief 



