788 NERVOUS SYSTEM OF THE HORSE 
olfactorii) which is connected with the lateral ventricle by a small canal inthe 
olfactory tract. The deep face is largely in contact with the frontal pole of the 
hemisphere and is connected with the olfactory tract. 
The gray matter of the bulb is external and is thickest on the convex anterior surface. The 
posterior part consists to a large extent of fibers which are the axones of the mitral cells of the 
deep layer of the gray substance and go to form the tract and striz. 
The olfactory tract (Tractus olfactorius)! is a very short but wide band of 
white substance which arises in the olfactory bulb and extends back to be continued 
by the olfactory striz. It contams a canal which connects the ventricle of the 
bulb with the lateral ventricle. 
The olfactory strie (Strive olfactorii)> are two in number. The lateral stria 
(Stria lateralis) is much the largest and most distinct. It passes backward, upward, 
and outward, widens out and joins the piriform lobe. — It is clearly defined dorsally 
by the sulcus rhinalis and is marked off from the trigonum olfactorium by the 
sulcus arcuatus. The medial stria (Stria medialis) is smaller, short, and not so 
Fic. 641.—Laterar View or Cast or Cavities oF BRAIN oF Horse. 
Bo, Cavity of olfactory bulb, which communicates through the canal J with a lateral ventricle; Ca, anterior horn, 
Cm, body, Ci, ventral horn of lateral ventricle; M, interventricular foramen which connects lateral and third ventricles; 
Ep, suprapineal recess, below which is the small infrapineal recess (not visible); Ro, optic recess; Rh, infundibular 
Fl, ridge corresponding to sulcus limitans; Rl, lateral recess, Rm, posterior 
(Dexler.) 
and pituitary recess; S, aqueduct; 
recess of fourth ventricle; Cc, beginning of central canal of spinal cord. 
well defined; it bends over to the parolfactory area on the medial face of the hemi- 
sphere below the genu of the corpus callosum.* 
The trigonum olfactorium is the prominent gray area situated in the angle of 
divergence of the medial and lateral olfactory striw. It is bounded laterally by the 
lateral olfactory stria, from which it is defined by the suleus arcuatus. It is con- 
tinuous with the area parolfactoria on the medial surface; behind the latter a band 
descends from the rostrum of the corpus callosum and is continuous below with the 
anterior perforated substance; it is termed the subcallosal gyrus (Gyrus sub- 
callosus). 
The piriform lobe (Lobus piriformis) is the well-marked prominence on the 
base lateral to the optic tract and cerebral peduncle, from which it is separated by a 
deep fissure. Its nipple-like apex lies behind the fossa lateralis and covers the 
optic tract. The external surface is marked by one or two sulci (lobi piriformis). 
The lobe contains a cavity, the ventral horn of the lateral ventricle. 
1Commonly termed the peduncle. *Commonly termed the tracts. 
3 An intermediate or middle stria has been described; its presence cannot be demonstrated 
in the horse. 
