798 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



Galeni. On the surface of the hemispheres are large veins which enter the 

 sinuses of the dura mater. 



The lymphatics form sheaths around the small blood-vessels. 



Development. — See " Embryology," for the development of the brain. 



Differential Characters in the Brain of the other Animals. 



In the animals which interest us, the brain presents differences with regard 



to volume, as might be sur- 

 ^'g- ^^"^^ mised from what has been stated 



in our general remarks, when 

 dealing with the cerebrum and 

 cerebellum ; in the arrange- 

 ment of the convolutions there 

 are also important differences. 



Ruminants (Figs. 442, 

 443). — In these creatures, the 

 brain is more globular than in 

 Solipeds. The hemispheres are 

 wider behind than in the Horse 

 and Ass, but they are narrower 

 in the frontal region ; there they 

 are a little flattened on each side, 

 and curved downwards. The 

 fissure of Sylvius is deeper at 

 its commencement ; its middle 

 branch, much more developed, 

 ascends to near the upper face 

 of the hemisphere ; at the 

 bottom of the latter is a V- 

 shaped plait, which unites the 

 ascending frontal convolution 

 to the second frontal convolu- 

 tion. This plait is concealed in 

 Solipeds. 



The large fissures are dis- 

 posed nearly as in the Horse ; 

 but it should be noted that the 

 fissure of Rolando is interrupted, 

 near its origin, by an annectent 

 gyrus which is thrown from 

 the curved plait on to the as- 

 cending frontal convolution, 

 and, in front, by another plait 

 that unites the first parietal 

 convolution to the limited fron- 

 tal convolution. 



The sigmoid gyi'us, or its 

 analogue, is concealed between 

 the passage plait that joins the parietal to the frontal convolutions. 



In the Sheep, the convolutions and the sulci on the surface of the brain are 



brain of the sheep (upper face), natural size. 



B, Medulla oblongata: 1, posterior pyramid of ditto. Ce, 

 Cerebellum : 2, 2, lateral lobes of ditto ; 3, middle lobe 

 of ditto. C, Right hemisphere of the brain. 12, Inter- 

 hemispherical fissure ; 13, 13, upper end of the fissure 

 of Sylvius; 14, 14, fissure of Rolando; 15, 15, postero- 

 inferior branch of ditto ; 16, 16, posterior branch of 

 ditto; 4, external parietal convolution; 5, internal 

 parietal convolution; 6, lob\ile of the curved plait; 7, 

 annectent gyrus uniting the frontal lobe to the lobule 

 of the curved plait, above the fissure of Sylvius; 8, 

 second frontal convolution ; 9, first frontal convolution ; 

 10, annectent gyrus uniting the first frontal convolution 

 to the second parietal conTolution ; 17, 17, crncial fissure. 

 G, G, Sigmoid gyrus. 



