HEAD AND NECK OF THE HORSE 207 



The floor of the ventricle is formed by the medulla oblongata and the 

 pons. Divided into two lateral halves by a median longitudinal groove, 

 the floor is further subdivided into areas. A longitudinal limiting 

 groove (sulcus limitans) forms the lateral boundary of an elongated 

 medial area. The limiting groove is shallow, but becomes a little 

 deeper at the anterior fovea '^ in the anterior half of the ventricle. The 

 elongated and slightly raised and rounded ridge between the median 

 and limiting grooves is the medial eminence (eminentia medialis), 

 which is most prominent on a level with the anterior fovea, where it 

 forms the colliculus facialis, so named from its association with part of 

 the root of the facial nerve. 



In the posterior part of the ventricle the limiting groove divides at 

 what is the equivalent to the posterior fovea of the human brain. Thus 

 the floor in this region is divided into three areas. (1) The hypoglossal 

 trigone (trigouura nervi hypoglossi) is the area between the fovea and 

 the median groove, and overlies the nucleus of the hypoglossal nerve. 

 (2) The ala cinerea, a triangular area between the two diverging 

 limbs of the limiting groove, is associated with the nucleus of the 

 glosso-pharyngeal and vagus nerves. (3) Lateral to the limiting groove 

 is the acoustic area (area acustica), which is continued into the floor of 

 the lateral recess of the ventricle. 



^ Fovea [L.], a small pit. 



[Cerebral Nerves, etc. 



