THE NERVOUS SYSTEM OF THE DOG 
849 
The cerebral hemispheres are very broad behind and diminish in width an- 
teriorly; there is a sudden narrowing at the frontal poles, which are flattened 
laterally. 
The tentorial surfaces are concave and form a deep cavity which re- 
ceives the anterior part of the cerebellum. 
The arrangement of the fissures and 
gyri is simpler than in the animals previously examined. 
The chief fissures are as follows: 
1. The lateral fissure extends upward and backward from the sulcus rhinalis a little behind 
the middle of the lateral surface of the hemisphere. 
2. The ectosylvian fissure has approximately the shape of an inverted U, and curves over 
the lateral fissure. It is regarded as consisting 
of three parts—anterior, middle, and posterior 
(F. ectosylvia anterior, media, posterior). 
3. The suprasylvian fissure lies above and 
approximately concentric with the preceding. It 
also consists of three parts—anterior, middle, 
and posterior. 
4. The ectomarginal or collateral fissure 
runs forward on the dorsal aspect of the hemi- 
sphere almost parallel with the dorso-medial bor- 
der. A little in front of the middle of the surface 
it gives off a short ansate fissure (F. ansata) 
which runs obliquely medially and forward. It 
is usually continued anteriorly by the coronal 
fissure, and may be in continuity posteriorly 
with the medilateral (or post-lateral) fissure. 
Fic. 679.—Brain Stem oF Doc; Dorsat VIEW. 
a, Spinal cord; 6, dorsal median groove; c, c’, funicu- 
lus gracilis; c’’, clava; d, d’, funiculus cuneatus; d’’, tuber- 
culum cuneatum; e, funiculus lateralis: e’, tuberculum cin- 
ereum; f, medulla oblongata; J, IJ, III, fovee of floor of 
fourth ventricle (fossa rhomboidea); g, limiting groove; h, 
median fissure; 1, eminentia medialis; k, ala cinera; J, I’, 
pons; m, posterior peduncle, and n, middle peduncle, of cere- 
bellum (cut); 0, anterior peduncle of cerebellum; p, p’, cor- 
pora quadrigemina, anterior and posterior; g, qg’, peduncles 
(brachia) of corpora quadrigemina; r, thalamus; s, massa 
intermedia; ¢, stria medullaris; u, anterior tubercle of 
thalamus; », pulvinar; w, corpus geniculatum laterale; z, 
corpus geniculatum mediale. (After Ellenberger, in Leiser- 
ing’s Atlas.) 
Longitudinal fissure 
Cerebellum 
Medulla 
oblongatg 
Fic. 680.—Brarn oF Doc; Dorsat VIEW. 
Fissures: i, Lateral; 2, ectosylvian; 3, suprasyl- 
vian; 4, ectomarginal (or collateral); 4’, ansate; 6, 
coronal; 6, ectolateral; 7, entomarginal; 8, presylvian 
(or orbital); 9, cruciate; 10, medilateral (separated 
from entomarginal on right side, but connected with it 
on left hemisphere); 11, f. prorex. 
5. The coronal fissure is usually the 
continuation of the ectomarginal. It runs 
forward and downward, curving around the 
cruciate fissure, and ends behind the middle 
of the presylvian fissure. 
6. The ectolateral fissure lies between 
the posterior part of the ectomarginal fissure 
and the suprasylvian fissure. 
7. The entomarginal fissure lies between the anterior part of the ectomarginal fissure and 
the dorso-medial border. 
It is often indistinct and not rarely absent. 
_ _8. The presylvian fissure—sometimes termed the orbital—begins at the sulcus rhinalis, 
a little in front of its middle, and curves over the anterior third of the lateral surface of the hemi- 
sphere in front of the coronal fissure. 
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