THE MESENCEPHALON. 



583 



Pedunculi Cerebri. The cerebral peduncles (Figs. 517 and 527) appear upon 

 the ventral or basal aspect of the mesencephalon as two large rope-like strands 

 which emerge from the cerebral hemispheres and disappear below by plunging 

 into the pars basilaris of the pons. At the place where each peduncle emerges 

 from the corresponding side of the cerebrum it is encircled by the optic tract. 



Each pedunculus cerebri is composed of two parts, viz., a dorsal tegmentaL part 

 (tegmentum), which is prolonged upwards into the region below the thalamus 

 (hypothalamus), and a ventral portion (basis pedunculi), which, when traced 

 upwards into the cerebrum, is seen to take up a position on the lateral side of 



Nucleus lentiformis 



Capsula interna (pars lenticulo-thalamica) 

 Nucleus caudatus 



Capsula interna 

 (pars lenticulo-v 

 caudata) 



Union of 



lentiform and 



caudate nuclei 



Tractub 

 olfactorius 



Tractus opticus^'' 



Infundibulum 



Hypophysis [anterior lobe " 

 cerebri ^posterior lobe 



Tuber cinereum ' ,. 



Corpus mainillare / 



Nervus oculomotorius ( 



Basis pedunculi'' 



Pons 



Nervus trigeminus (portio major 

 Nervus trigeminus (portio minor)'' ^ 

 Nervus facialis- 

 Nervus intermedius- 

 Nervus acusticus'' f 

 Nervus abducens '' 

 Nervus glossopharyngeus 



Nervus vagus 



Pyramis'" 



' Oliva--'' 



Fasciculus circumolivaris pyramidis 



Nucleus amygdalae (cut) 

 / 



Commissura anterior 



Stria terminalis 



Capsula interna (pars sublenticularis) 



Nucleus caudatus 



Thalamus 



Corpus geniculatum laterale 



Corpus pineale 



^Corpus geniculatum mediale 



Colliculus superior 



Brachium quadrigeminum 



inferius 



Colliculus inferior 



Lemniscus lateralis 

 Nervus trochlearis 





- -Brachium conjunctivum 



Brachium pontis 



-Fossa flocculi 

 _.Crus flocculi 



Nucleus dentatus 

 cerebelli 



Corpus ponto-bulbare 



Fasciculus spinocerebellaris 

 posterior 



Nervus spinalis 



FIG. 517. THE LEFT LATERAL ASPECT OF THE BRAIN-STEM AFTER THE CEREBRAL HEMISPHERE 



PT THE CORPUS STRIATUM) AND THE CEREBELLUM (EXCEPT THE NUCLEUS DENTATUS) HAVE BEEN REMOVED. 



the thalamus and to be continuous with the internal capsule of the brain ; and an 

 . intermediate part, the substantia nigra. When the base of the brain is examined, 

 '. it is the basis pedunculi which is seen, and it is observed to be white in colour and 



streaked in the longitudinal direction. In the tegmentum the longitudinally- 

 , arranged fibres are, in large part, corticipetal, or, in other words, fibres which are 



ascending towards the cortex of the cerebrum ; the basis pedunculi, on the other 

 , hand, is composed entirely of longitudinal strands of fibres which are corticifugal, 



or fibres which descend from the cerebral hemisphere. 



On the surface of the mesencephalon the separation between the tegmental and 



basal portions of the pedunculus cerebri is clearly indicated by a medial and a 



lateral groove. The medial furrow is the more distinct of the two. It looks 



38 c 





