296 George L. Streeter 



Peripherally the fibres from the ganglia of the roots together with 

 the remaining motor fibres that are not included in the accessory bundle 

 are collected into a common trunk and pass down caudally to be lost 

 in the ganglion nodosum. After they emerge at the distal end of this 

 ganglion they bend medialward and lose themselves on the wall of the 

 oesophagus. 



The n. trigeminus possesses the largest ganglion of the whole embryo. 

 From this ganglion the three large peripheral divisions extend ventral- 

 ward. The ophthalmic division passes forward and subdivides into the 

 frontal and nasociliary nerves, the latter forming a long slender well 

 defined branch passing just dorsal to the eye stalk. The maxillary and 

 mandibular divisions pass downward and break up in their terminal 

 branches among the cells of the maxillary process and mandibular arch 

 respectively. Centrally the ganglion is connected with the brain by 

 a thick short trunk which enters the wall at the pontal bend and opposite 

 the first and second rhombic grooves. Within the wall the fibres im- 

 mediately form a flattened longitudinal tract, as shown in Plate II, part 

 of which extends caudally as the spinal tract, and part extends forward 

 and upward to enter the cerebellar ridge. These fibres must be con- 

 sidered as containing both somatic and visceral elements, between which 

 no difference could be made out embryologically. 



In its motor elements the trigeminal nerve departs somewhat from the 

 type represented in the other three nerves of this visceral group. In 

 the others the nucleus of origin is in the basal plate, and the nerve 

 rootlets exhibit a characteristic curved course to reach the point of 

 emergence; while in the trigeminal the nucleus is more lateral and lies 

 directly against the entering sensory fibres, so that the fibres of the 

 motor root pass directly ventralward to fuse with the mandibular 

 division. 



It is possible that the motor nucleus of the trigeminal is to be con- 

 sidered as an hypertrophied example of one of the dorsal motor nuclei 

 found in the adult ninth and tenth nerves, both median and lateral to 

 the tractus solitarius^ and which have not yet been recognized in the 

 embryo. In that case we must conclude that either the nucleus ambiguus 

 and ventral motor root are not present in this nerve, or that they are 

 represented by the mesencephalic motor root. In analyzing these nerves 



Tor a description of the motor nuclei connected with the tractus solitarius 

 see E. L. Melius, '02. 



