Pons

[pons, bridge]. A proce or bridge of ti ue connecting two parts of an organ. P. cerebelli. Same as P. Varolii. P. Tarini, the posterior perforated space. P. Varolii, or simply Pons, a convex white eminence situated at the base of the brain, and serving to connect the various divisions with each other. It is placed in front of the medulla oblong at a, behind the cerebrum, and beneath the cerebellum, and rests upon the sphenobasilar groove. In structure the pons consists chiefly of nerve-fibers, but contains also areas of gray matter, the pontine nuclei. On section two portions, a superior and an inferior, are distinguishable. The latter contains transverse commi ural fibers and is traversed by the pyramidal tracts. The superior or dorsal portion of the pons consists largely of gray matter which is continued up from below, especially the formatio reticular is and the dorsal tracts of gray substance. In places the gray matter is grouped to form the nuclei of the fifth, sixth, seventh, and eighth nerves. In the lower part of the pons there is a small, folded gray ma , the superior olivary nucleus. It is enclosed by some transverse fibers known as the trapezium. The P. is connected with the medulla, with the cerebellum (by the middle peduncles), and with the cerebrum (by the crura cerebri). Pontile, 516