606 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



which brings it into connection with the Encephalic centres, is distinguished by 

 the peculiar arrangement of its fibrous strands and of its nuclei of gray mat- 

 ter; and also by the peculiar distribution and endowments of the nerves con- 

 nected with it. * The anatomical boundaries usually assigned to it are the 

 Pons Varolii above 1 and the Occipital foramen below; but these limits are 

 purely artificial, and for physiological purposes the course of its fibres must 

 be traced much higher. The part thus marked out has a bulblike form, 

 and presents, like the Cord of which it is the continuation, a posterior and 

 an anterior median fissure. The former is deep and narrow, extending to 

 the posterior border of a layer of commissural fibres which forms the floor 

 of the anterior fissure. The latter is wider and less deep ; and its continuity 

 with the anterior fissure of the Spinal Cord is interrupted by the decussation 

 of the Anterior Pyramids, which is marked externally by the crossing of 

 from three to five bundles of fibres from each side over to the other. This 

 decussation may be considered as the physiological boundary between the 

 Medulla Oblougata and the Spinal Cord. The surface of each lateral half 



is furrowed by grooves, which assist in 

 FIG. 212. marking out the several strands of nerve- 



fibres that may be distinguished on either 

 side : these are i. The Anterior Pyramids, 

 or Corpora Pyramidalia ; n. The Olivary 

 Bodies, or Corpora Olivaria ; in. The Lat- 

 eral Columns; iv. The Tubercles of Rolando, 

 or Tuberculi Cinerei ; v. The Restiform 

 Bodies, or Corpora Rediformia, otherwise 



Lateral view of tin- Medulla Oblongata: Called PrOGCSSUS a Cerebello Cld Medullaill 



ap, anterior pyramid ;o c, olivary column; Oblotlflatam; VI. The Posterior Pyramids, 



I c, lateral column ; t c, tubercle of Rolando, Qr Q )rpora Puramidalitt Posteriora. (See 



ortuberculo-cinereo; cr, corpus restiforrae; -,-,. n-tn rr\\ i- *i vu 



' ... Fig-. 212.) lie connections or these with 



op, posterior pyramid; a/, arciform fibres; , S VT i o i /~i 



Oil. Scrip., calamus scnptorius. the Brain above, and with the bpmal Cord 



below, will be presently traced. The vesic- 

 ular substance, on the other hand, is principally aggregated in three pairs 

 of ganglionic centres; of which the anterior forms the nucleus of the Olivary 

 body, the lateral of the Restiform, and the posterior of the Posterior Py- 

 ramidal. 



488. The Anterior Pyramids (i) consist entirely of fibrous structure and 

 establish a communication between the " motor tract" (Fig. 213, mt) of the 

 Crura Cerebri, and the anterior and antero-lateral columns of the Spinal 

 Cord. The principal part of their fibres decussate ; and these, as they pass 

 from above downwards, dip away from the anterior surface of the Cord, and 

 connect themselves with its middle or luti'rnl columns, instead of with its 

 anterior, as was pointed out by Rosenthal, 2 and more fully described by 

 Dr. J. Reid ; :i and some fibres are stated by Mr. J. L. Clarke, 4 to pass into 

 the posterior columns and posterior gray substance. A small part of the 

 fibres of the pyramidal columns, however, do not decussate, but proceed 

 downwards on the same side, into the corresponding anterior columns of the 

 Spinal Cord. 11. The Olivary bodies are composed of fibrous strands, inclos- 

 ing a large gray motor nucleus (Fig. 213, o a) on either side. The upward 



1 From which it is separated 1 literally in animals by ii broad band termed the Trti- 

 pe//min, but in man by a groove; the trape/ium tormini: the posterior border of the 

 1'uns. Sec L. Clarke, Proceed. Koy. Soc., vol. xi, p. 800. 



'-' Kin Ui'itriiL; /.nr Knrcphalotoinir, Weimar, 1815. 



:l Ivlinli. Meil. and Sun;. Journ., Jan. 18-11; and Physiol., Pathol., and Anut. 

 Researches, chap. vii. 



4 I'bil. Trans., 180S, p. 238; see also Meynert, op. fit , p. 5:28. 



