THE CENTRAL NERVOUS SYSTEM. 345 



foramen caecum (</). The dorsal (posterior) sulcus (Fig. 141, 

 a) is well marked ; it ends at the caudal boundary of the fourth 

 ventricle {h). 



The anterior lateral sulcus (Fig. 138, r) may be traced 

 craniad from the origin of the ventral roots of the first cervical 

 nerves {s), along the lateral border of the area elliptica (;/), 

 then curving mediad to the lateral border of the pyramis (<?), 

 and finally reaching the pons (/). Its position is marked by 

 the origin of the roots of the hypoglossal nerve (AY/). 



The posterior lateral sulcus (Fig. 141, b), marked on the 

 spinal cord by the origin of the dorsal nerve-roots, curves 

 laterad at the sides of the fourth ventricle (//) owing to the 

 increasing width of the latter, and ends at an elevated area of 

 oblique fibres, the area ovalis (/). 



The columns or funiculi bounded by the longitudinal 

 fissures present the following peculiarities: 



The anterior white funiculus of the cord is replaced in the 

 medulla by the pyramidal tracts (pyramides) (Fig. 138, o). 

 The pyramidal tracts are formed by fibres which emerge from 

 beneath the pons and pass caudad to disappear just craniad of 

 the level of the first cervical nerve {s). The pyramidal tracts 

 are bounded medially by the anterior median fissure (/), but 

 laterally each is separated from the anterior lateral sulcus (r) 

 over its caudal part by an elongated area elliptica (;/), the 

 human homologue of which is uncertain. It perhaps represents 

 the oliva. 



Laterad of the cranial portion of the pyrann'ds is an irreg- 

 ular area known as the trapezium (/) which abuts caudad on 

 the area elliptica («) and the area ovalis {in). The area Ovalis 

 (Fig. 138, in\ Fig. 141,/) (or zonula Arnoldi) is abroad band 

 of oblique fibres which passes from the lateral side of the area 

 elliptica craniodorsad to disappear under the cerebellum. 



The posterior white funiculus was divided in the cervical 

 region into two, the fasciculus gracilis (column of Goll) and 

 the fasciculus cuneatus (column of Burdach). The fasciculus 

 gracilis (Fig. 141, c) extends to the caudal end of the fourth 

 ventricle {h) and ends there in an expansion, the clava {d), 

 which forms the posterior boundary of the fourth ventricle. 



