NERVOUS SYSTEM. VERTEBRATA. 313 



Family EQUID^E. 



D. 402. The brain of a Horse (Equus caballus) . 



The Horse is about six times as big as a Man ; but in 

 spite of this fact its brain weighs less than one-half as 

 much as the human brain. 



In structure the brain may be regarded as a larger and 

 correspondingly more complicated Tapir's brain. The 

 cerebral hemispheres are relatively less rnacrosmatic than 

 the latter, and consequently only a very small area of the 

 great kidney-shaped lateral aspect of the hemisphere of the 

 Horse is formed of pyriform lobe. 



The " Sylvian fissure " is essentially of the same nature 

 as that of the Tapir, but there are usually two or more 

 compensatory sulci parallel to the chief " fissure/' which is 

 also relatively very short. The irregular H-shaped sulcus 

 found in the Tapir's brain (fig. 179) between the u Sylvian 

 fissure " and the postsylvian sulcus is here simplified and 

 prolonged to form part of an irregular arcuate sulcus like 

 the ectosylvian of the Cynoidea. It is not, however, homo- 

 logous to the latter, for, as Holl has shown, the " Sylvian 

 fissure " of the Horse is really formed by the ectosylvian 

 sulci. 



Then again the " anterior horizontal limb of the Sylvian 

 complex " is prolonged to form an enormous sulcus parallel 

 to and much longer than the orbital sulcus. 



The posterior horizontal ramus of the suprasylvian arc is 

 greatly elongated and gives off numerous branches. The 

 postsylvian sulcus is also large, and the great quadrilateral 

 area between it and the latter sulcus is rendered exceed- 

 ingly complicated by numerous irregular sulci. 



In addition to the typical lateral sulcus there are large 

 ecto- and entolateral sulci. On the mesial surface there is 

 a complete cingular arc (conjoint calcarine, intercalary, and 

 genual sulci), as in the Tapir. There is also a complete 

 subcingular arc (the so-called " sublimbic " sulcus of Guld- 

 berg) . 



Numerous secondary sulci, not present in the Tapir's 

 brain, have now made their appearance. On the whole, 



