724 NERVOUS SYSTEM. 



character of these cries as indicating the actual perception of painful impressions, and as 

 very different from cries that are purely reflex, according to the ordinary acceptation of 

 this term. Longet alludes to the voluntary movements and the cries observed in persons 

 subjected to painful surgical operations, when incompletely under the influence of an 

 anesthetic, concerning the character of which there can be no doubt. He regards the 

 movements as voluntary, and the cries as evidence of the acute perception of pain ; but 

 it is well known that such patients have no recollection of any painful impression, 

 although they have apparently experienced great suffering. As far as we can judge 

 from what we positively know of the functions of the encephalic centres, the pain under 

 these circumstances is perceived by some nerve-centre, probably the tuber annulare, but 

 the impression is not conveyed to the cerebrum and is not recorded by the memory. 



Taking all the experimental facts into consideration, the following seems to be the 

 most reasonable view with regard to the function of the tuber annulare as a nerve-centre : 



It is an organ capable of originating a stimulus giving rise to voluntary movements, 

 when the cerebrum, corpora striata, and the optic thalami, have been removed, and it 

 probably regulates the automatic voluntary movements of station and progression. Many 

 voluntary movements, the result of intellectual effort, are made in obedience to a stimu- 

 lus transmitted from the cerebrum, through conducting fibres in the tuber annulare, to 

 the motor conductors of the cord and the general motor nerves. 



The tuber annulare is also capable of perceiving painful impressions, which, when all 

 of the encephalic ganglia are preserved, are also conducted to and are perceived by the 

 cerebrum, and are remembered ; but there are distinct evidences of the perception of 

 pain, even when the cerebrum has been removed. 



Medulla Oblongata. 



The chief points of interest in the physiological anatomy of the medulla oblongata 

 relate to the direction of its fibres, their connection with the gray matter embedded in 

 its substance, and the course of the filaments of origin of certain of the cranial nerves. 

 Concerning the deep origin of the large root of the fifth, the motor oculi externus, facial, 

 pneumogastric, spinal accessory, and the sublingual, we shall have nothing to say in this 

 connection, as we have already treated of the physiological anatomy of these nerves with 

 sufficient minuteness ; and we have now to study the functions of the medulla oblongata, 

 and particularly its action as a nerve-centre. 



Physiological Anatomy of the Medulla Oblongata. The medulla oblongata is the 

 oblong enlargement which connects the spinal cord with the various encephalic ganglia. 

 It is about an inch and a quarter in length, and nearly an inch broad at its widest por- 

 tion. It rests in the basilar groove of the occipital bone, extending from the atlas to the 

 lower border of the tuber annulare, with its broad extremity above. Like the cord, it 

 has an anterior and a posterior median fissure. 



Apparently continuous with the anterior columns of the cord, are the two anterior 

 pyramids, one on either side. Viewed superficially, the innermost fibres of these pyra- 

 mids are seen to decussate in the median line ; but, if these fibres be traced from the 

 cord, it is found that they come from the white substance of its lateral columns, and that 

 none of them are derived from the anterior columns. The fibres of the external portion 

 of the anterior pyramids come from the anterior columns of the cord. At the site of the 

 decussation, the pyramids are composed entirely of white matter; but, as the fibres 

 spread out to pass to the encephalon above, they present nodules of gray matter between 

 the fasciculi. 



External to the anterior pyramids, are the corpora olivaria. These are oval and are 

 surrounded by a distinct groove. They are white externally and contain a gray nucleus, 

 called the corpus dentatum. 



