8^0 MAN 



tract laterally still remains uncovered and is situated between the ventral 

 surface of the inferior olivary nucleus and the lateral extremity of the ventral 

 lamina of the pontile nucleus. The jjontiU' nucleus contnnies to increase in 

 size and sends a ])rolongation around the uncovered lateral surface oi the 

 pyramidal tract w lilch, fusin<z; with the already established deep layer ol the 

 pontile nucleus, now forms a complete in\estment for the pyramidal tract. 

 The pontile nucleus m this region is divided into a massive structure ventrally 

 and a somew hat more reticulated collection of gray matter dorsally, which 

 begins to show channels through which stream the decussating fibers of the 

 middle cerebellar peduncle. The massive character ot the ventral layer ol the 

 pontile nucleus gradually loosens and becomes broken up into a vastly retic- 

 ulated series of laminae of gray matter separated by transversely crossing 

 pontile libers. 



As the nucleus assumes greatei proportions, it may be seen to form three 

 divisions, a ventral circumferential layer which is cjuite smooth and relatively 

 unbroken ventrallx , a deep transverse layer in contact with the tegmentum, 

 and an intermediate lace-like arrangement of nuclear material. The surface 

 layer of the j^ontih' nucleus, the stratum su])erliciale pontis, conforms to the 

 contour of the middle cerebellar peduncle, while the deep layer, the stratum 

 ])rofundum jjontis, is in direct contact with the tegmentum. Between these 

 two rather definite laminae may be seen disposed in a very irregular brandl- 

 ing maniur maii\ other la\ ers of gray matter, the stratum complexum pontis, 

 which is disposed traiisx ersel\' between the decussating fibers of the middle 

 cerebellar peduncle. These laminat- of gray matter continue upward irregu- 

 larly and as the u|)|)er jjortion of the pons is approached they tend to focus 

 ventrally and dorsall\, the dorsal grouj) joining the deep layer ol the pontile 

 nucleus, to form a support for the substantia nigra, while the \entral group 

 tends to coalesce ventrall\ and forms a thickeni'd mass of gra\ matter into 

 which the eeri'bral pt-duncle enters as it j^asses from the mesencei)halon into 



