800 



THE NERVOUS SYSTEM 



and continue directly into the spinal cord, to form there the ventral cerebro-spinal fasciculus or 

 direct pjTamidal tract. However, most of such fibres finally cross the mid-hne during their 

 course in the spinal cord. The exact proportion of tlie direct fibres is variable, but always the 

 greater mass of each pyramid crosses to the opposite side at the level of the decussation of the 

 pyramids, and descends the cord as the lateral cerebro-spinal fasciculus or crossed pyramidal 

 tract. Both of these pyramidal tracts are described in the discussion of the fasciculi of the 

 cord. 



Fig. 629. — Semi-diagrammatic Representation of the Ventral Aspect of the Rhomben- 

 cephalon AND Adjacent Portions of the CEREBRUM.^(Modified from Quain.) 



Insula 



Olfactory tract 



Hypophysis 

 / 



Mammillary bodies 



Cerebral peduncle 



Semilunar (Gasser 

 ian) ganglion 



Oblique fasciculus 

 of pons 



Tuber cinereum 



Oculomotor nerre 

 (lU) 



Lateral geniculate 

 body 



"-~- Trochlear nerve (IV) 



Masticator nerve 

 (motor root of tri- 

 geminus) 



Trigeminus (V) 



. Abducens (VI) 



— Brachium of pons 



— Facial nerve (VII) 



~^ Glosso-palatine nerve 

 {intermediate part of 

 ^\ facial) 



Cochlear and vestibular 

 \ nerves (Acoustic or VIII) 



Glosso-pharyngeal nerve (IX) 

 Vagus nerve (X) 



\ Accessory nerve (XI) 

 (spinal accessory) 



Hypoglossal nerve (XII) / 



Pyramid 



Decussation of pyramids^ 



Cervical I 



Cervical II 



Each pyramid is bounded laterally by the antero -lateral sulcus, also continu- 

 ous with that of the same name in the spinal cord. Toward the pons this sulcus 

 separates the pyramid from the olive [oliva] (inferior olivary nucleus), and in the 

 region of the olive there emerge along this sulcus the root filaments of the hypo- 

 glossal nerve. These are in line with the filaments of the ventral roots of the spinal 

 nerves. The olives, as their name implies, are oblong oval eminences about 1.2 

 cm. in length. They extend to the border of the pons, and are somewhat thicker 

 at their upper ends. Their surfaces are usually smooth, except at their lower ends, 

 where they frequently appear ribbed, owing to bundles of the external arcuate 

 fibres passing across them to and from the restiform body, which occupies the 

 extreme lateral portion of the medulla. Along the line between the restiform body 

 and the olive are attached the root filaments of the vagus, glosso-'pharyngeal, 

 and spinal accessory nerves. Both the abducens and the facial nerve emerge along 

 the inferior border of the pons, the facial in line with the glosso-pharyngeal, but 

 the abducens in line with the liypoglossus. 



Dorsal aspect.^-The incr(!ascd lateral diameter of the medulla oblongata is 

 contributed to a great extent by the restiform bodies. These are the inferior cere- 



