82 JoURNAL OF COMPARATIVE NEUROLOGY. 
penetrate, to finally emerge as the motor: roots of their respec- 
tive nerves. 
The dorsal cornu of the cord is continued into the oblon- 
gata in an enlarged condition, and it becomes associated with 
sensory fibres of the V, IX, and X nerves to form the general 
cutaneous nucleus (Fig. 2, g. c. z.). The neurones of this nu- 
cleus provide a primary termination for certain general cutaneous 
fibres; while others turn backward to the cord as the spinal V. 
tract. At the posterior levels of the oblongata this system 
appears dorsal to all other structural features, the pair forming 
the rounded, crest-like margins to the fourth ventricle. Pro- 
ceeding anteriorly, the nucleus is pushed into a position both 
more ventral and more lateral by the superposition of a new 
structure, the tuberculum acusticum. 
The tuberculum acusticum is shown in Figs. I and 2, ¢. a. 
It extends posteriorly from the restiformis along the lateral 
margin of the fourth ventricle some three quarters of the dis- 
tance to the calamus scriptorius, tapering as it proceeds. It is 
separated from the general cutaneous nucleus below it by a 
fissure which reaches well toward the limitans interna. The 
outer zone of the acusticum is structurally continuous with the 
cerebellum; it is known as the cerebellar crest (Fig. 2, cd. cr.). 
The acusticum is the centre for the nerves of the lateral line 
sense-organs and the internal ear. Its interpretation will be 
considered in Subsection 7. 
2. Review of Nerve Components. 
A proper point of view for the structure of the oblongata 
can best be obtained through familiarity with the problems of 
the cranial nerves pertaining to this region of the brain. Refer- 
ence to the text-books of descriptive anatomy will discover 
hardly a trace of the conceptions which dominate the modern 
morphology of nerves. The discovery made by Sir CHARLES 
BELL as to the character of the dorsal and ventral roots of the 
spinal nerves was one which represented a distinct advance in 
sound physiology, but the application of BELL’s formula to the 
cranial nerves has not been productive of sound morphology. 
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ee 
