128 



FUNCTIONS OF THE NERVOUS SYSTEM. 



Fig. 22. 



the anterior columns of the 

 spinal marrow ; 7, the lateral 

 columns. 



been supposed to be the peculiar seat of vitality ; but 

 the only real foundation of this idea is, that it is the 

 great centre of the Respiratory actions, on the con- 

 tinuance of which all the other functions are depend- 

 ent. The Brain may be removed from above, and 

 nearly the whole Spinal Cord from below, without an 

 immediate check being put upon all the phenomena 

 of life. In this Medulla Oblongata,/owr different parts 

 maybe distinguished on each side ; 1, The Anterior 

 Pyramids, or Corpora Pyramidalia ; 2, The Olivary 

 bodies, or Corpora Olivaria ; 3, The Restiform bodies, 

 or Corpora Restiformia, otherwise called Processus 

 a Cerebello ad Medullam Oblongatam; 4, The Pos- 

 terior Pyramids, or Corpora Pyramidalia Posteriora. 

 The connections of these with the Brain above, and 

 with the Spinal Cord below, will be now traced.* 



An anterior view of the Me- 169. As our object, however, is rather Physiolo- 



duiia Obiongata and of the ter- -^ t j ian p ure }y Anatomical, we shall commence with 



a description of the motor and sensory tracts, which 



Mitischelh. 1. the pons va- r J . ' 



roiii; 2, the emminentia oiiva- may, according to Sir C. Bell,t be very distinctly sepa- 

 ria; 3, the corpus pyramkiaie ; rated in the Pons Varolii. The Pons has been correctly 

 4, the corpus restiforme ; 5, the designated as the great Commissure of the Cerebel- 

 decussation of Mitischeiii; 6, j um? enclosing the Crura Cerebri ; and its transverse 

 fibres not only surround the longitudinal bands which 

 connect the Cerebrum with the Spinal Cord, but pass 

 through them, so as in some degree to isolate the two 

 lateral halves from one another, and to form a complete septum between the 

 anterior and posterior portions of each. The Motor tract is brought into view, 

 by simply raising the superficial layer of the Pons, and tracing upwards and 

 downwards the longitudinal fibres which then present themselves. It is then 

 found, that these fibres may be traced upwards, chiefly into the Corpora Striata, 

 whence they radiate to the Hemispheres ; and downwards, chiefly into the An- 

 terior Pyramids. From this tract arise all the Motor nerves usually reckoned 

 as Cerebral ; as will be seen in the accompanying Figure. The Sensory 

 tract is displayed, by opening the Medulla Obiongata on its posterior aspect ; 

 and then separating and turning aside the Restiform Columns, so as to bring 

 into view the Posterior Pyramids which lie on the outside of the calamus 

 scriptorius. On tracing their fibres upwards, it is found that they form a part 

 of the posterior layer of the Crura Cerebri, ultimately passing on to the Thalami 

 nervorum opticorum, whence they radiate to the Hemispheres. From this 

 tract, no motor nerves arise ; but on tracing it downwards into the Spinal 

 Cord, it is found that the sensory root of the fifth pair terminates in it, and 

 that the posterior roots of the spinal nerves are evidently connected with its 



* Great diversities will b,e found in the accounts given of these connections by differ- 

 ent authors ; some of which are attributable to a variation in the use of terms, which 

 must not pass unnoticed. By the majority of Anatomists, the name of Corpora Reslifor- 

 mia is given to the Cere.bellar Columns; and this designation, therefore, it seems advisa- 

 ble to retain. Some, however, and amongst them Dr. J. Reid, in his late very excellent 

 desertion of the Anatomy of the Medulla Obiongata, (Edinb. Med. & Surg. Journal, 

 Jan. 1841,) give the name to the columns that pass up from the posterior division of the 

 spinal cord into the crus cerebri, which are here called (after Sir C. Bell) the posterior 

 pyramids; and apply the term Posterior Pyramids to the Cerebellar column. The truth 

 is that, as Sir C. Bell has justly observed, all the tracts of fibrous matter connecting the 

 Brain with the Spinal Cord have a somewhat pyramidal form; and it might be added 

 that all have something of a restiform or cord-like aspect. 



j- Philosophical Transactions, 1835. 



