764 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



actually forms an intermediate bond between the three enlargements which form 

 the principal mass of the organ. 



The cranial portion of the central nervous mass is, then, composed of three 



Fig. 423. 



BRAIN OF THE HORSE (UPPER SURFACE). THRKE-FOURTHS THE NATURAL SIZE. 



1, Great longitudinal ov inter-hemispherical fissure; 2, 2, crucial fissure; 3, 3, fissure of Rolando. 

 4, 4, its anterior branch ; 5, 5, its posterior branch ; 6, 6, plaits of the ascending frontal convolu- 

 tion ; 7, 7, the two pl:iits of the external parieto-occipital convolution ; 8, 8, internal parieto- 

 occipital convolution; 9, 9, first frontal convolution; 10, 10, second frontal convolution; 11, 11, 

 sigmoid gyrus, often concealed by the annectent gyrus of 12, which joins the ascending frontal convo- 

 lution of the second frontal ; 13, lobule of the curved plait; 14, 14, annectent gyrus uniting the two 

 parietal convolutions to the sigmoid gyrus, and through it to the frontal convolutions, o, 0, 

 Olfactory bulbs; B, medulla oblongata; c', middle lobe of the cerebellum; C^, lateral lobes of 

 ditto. 



apparatuses : the isthmus of the brain — a prolongation of the spinal cord ; and the 

 cerebellum and cerebrum — bulbous lobes grafted on the superior face and anterior 

 extremity of this peduncle. These three divisions are very well seen in their 



