THE NERVOUS SYSTEM OF THE PIG 



721 



gemina are wide apart, rounded, and relatively large. The internal geniculate 

 body is prominent. The cerebral hemispheres are somewhat bean-shaped in 

 lateral profile, the convex border being dorsal. The arrangement of the gyri 

 and sulci is simi)ler tlian in the horse or ox. The principal fissures are as 

 follows : 



1. The lateral fissure (of Sylvius) begins at the sulcus rhinalis and runs upward 

 and somewhat backward on the depressed part of the lateral surface of the hemi- 

 sphere; it appears unbranched on superficial examination, but when the gyrus 

 which almost completely conceals the insula is raised, an anterior branch is exposed 

 which forms the dorsal l)0undary of the insula. 



2. The suprasylvian fissure pursues a curved course approximately^ parallel 

 with the dorso-medial border of the hemisphere. Its posterior end is separated by a 

 short interval from the sulcus rhinalis posterior. From its highest point a branch 

 proceeds obliquely upward and forward, crosses the dorso-medial liorder, and 

 joins the splenial fissure. 



3. The diagonal fissure crosses the anterior part of the lateral surface. It is 

 directed obliquely downward and backward. 



4. The coronal fissure is constant and deep. It is directed upward and inward 

 over the frontal pole, continues backward near the 



dorso-medial border, and usually ends by passing 

 obliquely over the border to the inner surface of the 

 hemisphere. 



5. The presylvian fissure begins — apparently as 

 a branch of the sulcus rhinalis anterior — about 2 cm. 

 in front of the lateral fissure, and curves over the 

 lateral aspect of the frontal pole. 



6. The marginal fissure begins behind the cruci- 

 ate fissure close to the dorsomedial border and ex- 

 tends in a gentle curve backward almost to the occi- 

 pital pole. 



7. The ectomarginal fissure lies above and 

 nearly parallel to the posterior part of the supra- 

 sylvian fissure. 



8. The entomarginal fissure lies along the pos- 

 terior part of the dorso-medial liorder. 



9. The calloso-marginal fissure consists of two 

 separate parts. The more extensive posterior part 

 is termed the splenial fissure. It extends from the 

 tentorial aspect of the hemisphere in a direction 

 parallel with the corpus callosum nearly to the middle 

 of the medial surface ; it is continued by the cruciate 



fissure and is also connected with the suprasylvian and coronal fissures by liranches 

 which pass obliquely upward and forward. The anterior part, the genual fissure, 

 lies about midway between the anterior part of the corpus callosum and the dorso- 

 medial border. 



10. The cruciate fissure is short and shallow. It runs obliquely upward and 

 forward from the anterior end of the splenial fissure on the inner surface of the 

 hemisphere. 



11. The sulcus rhinalis extends in an undulating manner along the entire 

 lower part of the lateral surface of the hemisphere and forms the upper limit of the 

 rhinencephalon. 



The olfactory bulbs are very large and the tracts extremely broad and short. 

 The trigonum olfactorium is so prominent as to be termed the tuberculum olfac- 

 torium. 



46 



Fig. 534. — Cerebral Hemispheres 

 OF Pig, Dorsal View. 

 a. Upper part of lateral fissure 

 (of Sylvius); b, cruciate fissure; c, 

 suprasylvian fissure, with its anterior 

 branch (c') and upper branch (c"); 

 d, diagonal fissure; e, coronal fissure; 

 /, presylvian fissure; a, marginal 

 fissure; h, ectomarginal fissure; i, 

 entomarginal fissure. (After EUen- 

 berger, in Leisering's Atlas.) 



