264 



INNERVATION. 



[CHAP. X. 



Fig. 68. 



posterior fissure extends to the posterior surface of this commissure, 

 there being no such transverse lamina of vesicular matter in the 

 medulla as in the cord. 



When the pia mater has been carefully removed from the surface 

 of the medulla oblongata, certain grooves are seen which indicate a 

 subdivision of the organ, which is convenient for the purposes of de- 

 scription. In front are the anterior pyramids (corpora pyramidalia 

 antica] separated from each other along the middle line by the ante- 

 rior fissure. External to each anterior pyramid there is an oval 

 prominence surrounded by a superficial groove, which in some in- 

 stances is partially interrupted by some arciform fibres which cross 

 it at its lower part. These projections are the olivary bodies. 

 External to these, and forming the lateral and a great part of the 

 posterior region of the medulla oblongata, are the restiform bodies, 

 two thick columns of fibrous matter, which are separated from each 

 other along the middle line by two slender columns, the posterior 

 pyramids. These last bound the posterior fissure. 



The anterior pyramids are bundles of 

 fibrous matter which extend between the 

 antero-lateral columns of the cord and 

 the cerebral hemispheres. Below the me- 

 socephale the fibres are compactly applied 

 to each other so as to form on each side of 

 the median line a column of white matter, 

 the transverse section of which has more 

 or less of a triangular outline. Traced up- 

 wards, the pyramids are found to pass into 

 the mesocephale above its inferior layer of 

 transverse fibres, the pons Varolii. At its 

 entrance into this part of the brain each 

 pyramid experiences a slight but well- 

 marked constriction, but immediately ex- 

 pands again ; and its fibres in their further 

 course upwards gradually diverge, and 

 contribute to form the inferior lamina of 

 the crus cerebri. 



In their ascent through the mesocephale the fibres of the pyra- 

 mids are crossed at right angles by some deep transverse fibres on 

 different planes which belong to the same system as those which con- 

 stitute the pons. With these fibres those of the pyramids interlace. 

 Vesicular matter is deposited in the intervals between the more deep- 

 ly seated fibres, from which probably some fibres take their origin, and 



Front view of the medulla oblon- 

 gata: p, p. Pyramidal bodies, de- 

 cussating at d. o. o. Olivary bodies. 

 r, r. Restiform bodies, a, a. Arciform 

 filnvs. v. Lower fibres of the Pons. 

 Varolii, 



