280 



NORMAL HISTOLOGY. 



oblongata, is the uninterrupted upward prolongation of the spinal cord and 

 above is limited by the projecting lower border -of the quadrilateral mass of 

 the next division, \\\e pons Varolii. Beyond the upper margin of the pons, 

 the brain-stem is represented by a third division that ventrally is separated 

 by a deep recess into two diverging limbs, the cerebral peduncles, or crura 

 cerebri, to correspond with the halves or hemispheres of the cerebrum. 

 Each of these receives one of the crura and in this manner is connected with 

 the lower levels of the cerebro-spinal axis. The greater part of the medulla 

 and pons is covered dorsally by the cerebellum, whose large lateral expan- 

 sions, or hemispheres, project on either side as conspicuous masses, distin- 



Orbital surface of 

 frontal lobe 



Optic commissure 



Optic tract 



Cerebral peduncle 



Interpeduncular space 



Cerebellum 



Olfactory tract 



Stalk of pituitary body 



Tuber cinereum 

 Mammillary bodies 

 Cerebral peduncle 

 Temporal lobe 

 Pons 



Cerebellum 



Occipital lobe 



Spinal cord 



FIG. 327. Human brain, viewed from below, showing relations of brain-stem to spinal cord and cerebrum, 

 as well as more prominent details of brain. 



guished by the closely set plications and intervening fissures that mark their 

 surface. Of the five component parts of the brain medulla, pons, cerebral 

 peduncles, cerebrum, and cerebellum the last two are coated with the cor- 

 tical gray matter, in which, broadly speaking, are situated the neurones that 

 constitute the end-stations for the sensory impulses conveyed by the various 

 corticipetal paths and the centres controlling the lower-lying nuclei of the 

 motor nerves. The brain-stem, on the other hand, whilst containing numer- 

 ous stations for the reception and distribution of afferent impulses, is pri- 

 marily the great pathway by which the cerebrum and the cerebellum are 

 connected with each other and with the spinal cord. 



Viewed in a mesial sagittal section (Fig. 328), each of these divisions is 

 seen to be related to some part of the system of communicating spaces that, 

 as the lateral and third ventricles, the aqueduct of Sylvius and the fourth 

 ventricle, extend from the cerebral hemispheres above, through the brain- 



