788 



NERVOUS SYSTEM OF THE HOHSE 



olfactorii) which is connected with the lateral ventricle by a small canal in the 



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 tliickest on the convex anterior surface. The 

 posterior part consists to a large extent of fibers which are the axones of the mitral oeUs of the 

 deep layer of the gray substance and go to form the tract and striae. 



The olfactory tract (Tractus olfactorius)i jg ^ ygj-y short but wide band of 

 white substance which arises in the olfactory bulb and extends back to be continued 

 by the olfactory strise. It contains a canal which connects the ventricle ^of the 

 bulb with the lateral ventricle. 



The olfactory striae (Striae 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 



Fig. 641. — Lateral View of Cast op Cavities of Brain of Hohse. 

 Bo, Cavity of olfactory bulb, which communicates through the canal / 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 

 and pituitary recess; S, aqueduct; Fl, ridge corresponding to sulcus limitans; Rl, lateral recess, Rm, posterior 

 recess of fourth ventricle; Cc, beginning of central canal of spinal cord. (Dexler.) 



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 striae. It is bounded laterally by the 

 lateral olfactory stria, from which it is defined by the sulcus 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 g3rrus (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. 



' Commonly termed the peduncle. ^ Commonly termed the tracts. 



' An intermediate or middle stria has been described ; its presence cannot be demonstrated 

 in the horse. 



