118 ANTHROPOLOGY. 
or semilunar. The two former are connected by the tortuous transverse 
laminz of the superior vermiform process, and the two posterior by those 
forming the floor of the posterior notch: d. The median portion presents 
the single or azygos superior median lobe or vermiform process. e. The 
interior surface of each hemisphere presents five lobes. Most anterior and 
distinct from the hemisphere are: first, the flocculus or pneumogastric lobule, 
connected to its fellow and to the nodule by the inferior medullary velum ; 
second, the tonsilic lobe or amygdalar, on the side of the ventricle, and con- 
nected to the opposite through the uvula or spigot; third, the digastric; 
fourth, the gracilis; fifth, the semilunar, which is joined to its fellow by the 
convex transverse laminze at the bottom of the posterior notch; sixth, the 
inferior median lobe, or vermiform process, presents from before backwards 
three lobules; the nobule most anterior, next the uvula or spigot, and 
posteriorly the pyramid. 
The fourth ventricle is a lozenge-shaped cavity, situated in the upper and 
posterior part of the medulla oblongata, and formed by the separation of its 
postero-lateral columns (corpora restiformia). The cerebellum contributes 
to inclose it by means of the anterior laminz of the superior vermiform 
process and the valve of Vieussens, and below and behind by the inferior 
vermiform process. 
5. MEDULLA OBLONGATA. The medulla oblongata, or spinal bulb, is that 
conical portion of white substance which extends from the lower margin of - 
the pons Varolii to the spinal cord, on a level with the ring of the atlas. 
Its upper end or base, though apparently limited by the pons, is prolonged 
upwards through it to the crus cerebri of each side. Inferiorly, there is no 
distinction between it and the spinal cord posteriorly or laterally. It pre- 
sents an anterior and posterior median fissure, which divides it into two 
symmetrical portions, each of which is marked by three grooves and four 
convex eminences, viz. the anterior pyramid, the corpora olivaria, the cor- 
pora restiformia, and the posterior pyramid. 
The posterior fissure is continuous with that-of the spinal cord. It is 
narrow, deep, and lined by the pia mater. The anterior fissure, the con- 
tinuation of the spinal, is broader but shallower, and lined by transverse 
commissural fibres. Nearly an inch below the pons this fissure is inter- 
rupted by the decussating fasciculi, three or four in number, which ascend 
obliquely inwards from the lower end of each pyramid to the opposite one, 
interlacing or interdigitating with each other. 
The anterior pyramids are two narrow, convex, white bands, about an 
inch long, small inferiorly, and partially united by the decussating fasciculi. 
They appear to be the direct as well as decussating medium of communi- 
cation between the anterior fibres of the cord, the mesocephalon, crura 
cerebri, corpora striata, and cerebral hemispheres. 
The corpora olivaria are smaller and shorter than the pyramids, are 
external and posterior to these, and separated by a groove both from them 
and from the restiformia. They only exist in man and quadrumana. 
White and fibrous externally, when divided they present a mass of grey 
neurine called olivary ganglion or corpus dentatum. 
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