810 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



olfactory lobes; behind them come the cerebral lobes covering the 

 corpora striata, and the third and usually the largest mass, correspond- 

 ing to the optic thalami and corpora quadrigemina ; behind them is seen 

 the cerebellum as a small central mass, while the medulla oblongata is 

 the connecting link between the spinal cord below and the basal ganglia 

 of the brain above. These different parts of the brain will be taken up 

 in turn, commencing with the medulla oblongata as the cranial 

 prolongation of the spinal cord. 



1. Medulla Oblongata. — The medulla oblongata, like the spinal 

 cord, is composed of two symmetrical halves, each capable of separation 



fn- 



Fig. 351.— Section of the Decussation of the Pyramids. {Landois.) 



f.I.a., anterior median fissure, displaced laterally by the fibres decussating at d ; V, anterior column ; 

 C.a., anterior corau, with its nerve-cells, a, b ; rr, central canal ; S. lateral column ; />., fonnatio retic- 

 ularis; re, neck, and, g, bead of the posterior corau ; r.p.C.I., posterior root of the first cervical nerve: 

 n.c, first indention of the nucleus of the funiculus cuneatus : n.g., nucleus (clava) of the funiculus gra- 

 cilis ; Zfl, funiculus gracilis; 7/2, funiculus cuneatus; s.f.p., posterior median fissure; x, groups of gangli- 

 onic cells in the base of the posterior cornu. 



by the naked eye into three different divisions, the anterior pyramids, 

 the olivary and restiform bodies, and the posterior pyramid, or funiculus 

 gracilis. The lower end of the medulla oblongata, at the point of exit 

 of the roots of the first cervical nerves, is characterized b_y a deviation 

 of the lateral columns (crossed pyramidal tract) of the cord, which, up 

 to this point running parallel with the axis of the cord, here turn in 

 through the gray substance of the anterior horn and cross to the oppo- 

 site side of the cord in the anterior white commissure to join the direct 

 pyramidal tract. The lateral columns of the cord consequently form a 

 decussation at the bottom of the anterior longitudinal fissure in the 



