5i2 THE BRAIN 



cephalon, and they decussate with each other across the median plane and 

 proceed upwards to the red nuclei. 



The term leinnisciis (O.T. fillet} is given to two tracts presenting very 

 different connections. The medial leniniscus (Figs. 211 and 212) is a 

 sensory tract passing upwards to the thalamus. The lateral knmiscus 

 belongs to the auditory apparatus, and is a part of a chain through which 

 the cochlear nuclei establish connection with the inferior quadrigeminal 

 body and the medial geniculate body. The lateral lemniscus can be 

 readily detected as it emerges from the upper part of the lateral sulcus of 

 the mid-brain, and passes, postero- superiorly, to the lower border of the 

 inferior quadrigeminate body and inferior brachium. It has the form of 

 a raised triangular band which encircles the lateral surface of the upper 

 end of the brachium conjunctivum (Fig. 221). 



Within the upper part of the tegmentum there is a collection of nuclear 

 matter which is termed the nucleus ruber, from its ruddy appearance 

 when seen in section. It is rod-like in form, and extends upwards into the 

 tegmental region below the thalamus. In transverse section it presents a 

 circular outline, and it is closely associated with the upward prolongation 

 of the fibres of the brachia conjunctiva cerebelli. The brachium conjunc- 

 tivum cerebelli is an efferent tract from the nucleus dentatus of the 

 lateral hemisphere of the cerebellum, and its fibres end in the red nucleus 

 and the pulvinar of the thalamus of the opposite side. The tegmentum 

 of the pedunculus cerebri may be considered to consist of two parts : viz. , 

 a lower part, which is subjacent to the inferior quadrigeminal bodies, 

 and is largely occupied by the decussation of the brachia conjunctiva 

 cerebelli ; and an upper part, subjacent to the superior quadrigeminal 

 bodies, which is traversed by the emerging bundles of the third nerve, 

 and contains the nucleus ruber. 



BASAL GANGLIA OF THE CEREBRAL 

 HEMISPHERES. 



The basal ganglia of the cerebral hemispheres must now 

 be examined. They are the caudate and lentiform nuclei, 

 which together form the corpus striatum ; the claustrum ; 

 and the amygdaloid nucleus. With these it is necessary to 

 study also the composition of the thalamus and the external 

 and internal capsules. 



Dissection. The right and left portions of what remains of the cerebrum 

 should be separated from each other by a median incision. On the left 

 portion the sulci and gyri on the lower surface of the hemisphere may be 

 examined, if this has not been done already on another specimen. 



A series of sections should, in the next place, be made through both the 

 right and left portions of the cerebrum, with the view of displaying the basal 

 ganglia. On the right side remove a succession of thin slices by carrying a 

 long knife in a horizontal direction through the parts which form and lie below 

 the floor of the central part of the lateral ventricle. It is not advisable to 

 proceed farther down than the level of the anterior commissure. 



On the left side of the brain a series of vertical-transverse or frontal 

 sections should be made through the remaining portion of the cerebrum. 



