800 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



backwards, describes a marked curve with concavity antero-inferior, then returns 

 forwards, and terminates by two branches at some distance from the sigmoid 

 gyrus, from which it is separated by a plait that unites — as in Ruminants — the 

 first parieto-occipital convolution to the anterior convolutions. The result of 

 this arrangement is that the frontal lobe extends well backwards on the external 

 face of the hemisphere. On the other hand, the convolution that occupies the 

 position of the lobule of the curved plait is much reduced ; it communicates by an 

 annectent gyrus with the parieto-occipital lobe. The latter occupies two-thirds of 

 the upper face of the hemisphere ; it is limited in front by a very evident criccial 



Fig. 445. 



LATERAL FACE OF THE DOG'S BRAIN. A, MASTIFF ; B, BULLDOG. 



1, Inter-hemispherical fissure; 2, crucial fissure; 3, fissure of Sylvius; 4, fissure of Rolaudo; 5, 

 olfactory bulb; 6, temporal lobe; 7, 7, sigmoid gyrus; 8, 9, the two convolutions of the parieto- 

 occipital lobe; 10, convolution of the curved plait; 11, 12, the two plaits of the ascending frontal 

 convolution ; 13, 14, frontal convolutions ; 15, annectent gyrus uniting the ascending frontal to the 

 frontal convolutions ; 16, plait uniting the external parietal to the frontal convolutions ; 17, 

 annectent gyrus uniting the internal parietal convolution to the sigmoid gyrus. C, Cerebellum ; Bu, 

 medulla oblongata; P, Pons Varolii. 



fissure and a sigmoid gyrus. The temporal lobe is well defined ; its parallel sulcus 

 is completely effaced. 



To sum up : in the Dog, the lobes and lobules observed iu Solipeds and Rumi- 

 nants are found ; their relative extent alone is changed. A word has to be said 

 with regard to the frontal and parieto-occipital lobes. The first is enveloped by 

 an ascending frontal convolution that describes a ^ery sudden flexuosity, and 

 enters the sigmoid gyrus. The second frontal convolution immediately surrounds 

 the middle branch of the Sylvian fissure ; behind, it has the same relations with 

 the ascending convolution as in the Horse ; in front, it passes into that convolu- 

 tion. Lastly, the first frontal convolution is, like the orbital lobe it surmounts, 



