42 



{k) The medulla oblongata, broad anteriorly, but narrower posteriorly. 

 Note— 



(1) The ventral pyramids, on either side of the ventral fissure of 



the spinal cord. 



(2) The olivary bodies, one on each side, external to the ventral 



pyramids. 



(3) The trapezoid bodies, bands of transverse fibres, each at the 



external side of the ventral pyramids anteriorly. Note the 



abducent nerve (6th cranial), arising from the medulla close 



to the middle line, and just behind the pons Varolii ; the 



facial (7th cranial), from the outer side of the corpus trape- 



zoideum anteriorly ; the auditory (8th cranial), immediately 



behind this; the glosso -pharyngeal and pneumogastric 



(9th and 10th cranial), from the side of the medulla by 



many small roots; the spinal accessory (llth cranial), 



behind this, arising by about ten small roots ; and the 



hypoglossal (I2th cranial) from near the middle line by 



several small roots. 



The cavities of the brain, and structures connected with them. Make 



a longitudinal vertical section of the brain in the middle line, and 



observe — 



(a) The corpus callosum connecting the two cerebral hemispheres in the 



middle line. 

 (6) The fornix below the corpus callosum, continuous with the corpus 

 callosum posteriorly, but separated from it anteriorly by the cavity 

 of the " fifth " ventricle. 

 (c) The third ventricle, bounded above and in front by the velum inter- 

 positum. In connection with this ventricle note — 



(1) The anterior commissure, a small transverse band of fibres in 



its anterior wall in front of the fornix. 



(2) The middle commissure, a very thick band extending across 



the middle of the ventricle, and connecting the two optic 

 thalami. 



(3) The posterior commissure, a small transverse band of fibres in 



the posterior wall of the ventricle, immediately in front of the 

 corpora quadrigemina. 



(4) The foramen of Monro, which brings the anterior part of the 



ventricle into communication with the lateral ventricles. 

 Remove horizontal slices of one cerebral hemisphere to expose 

 the lateral ventricle, and observe the grey (cortical) matter, 

 the white (medullary) matter of the hemisphere, and at a 

 deeper level the corpus Striatum. 



(5) The stalk of the pineal body, an upward continuation of the 



third ventricle. 



