THE CRANIAL NERVES. 538 



root lies in close relation with Froriep's ganglion, fg, and a very 

 little distance in front of the first cervical nerve ; while the 

 most anterior root lies just behind the pnenmogastric nerve. 

 The cervical roots of the spinal accessory nerve do not appear 

 until a later stage, a probable indication that the spinal accessory 

 is to be regarded as a cranial rather than as a spinal nerve. 



The motor roots of the pneumogastric, or tenth cranial nerve 

 (Figs. 227 and 228, XM). These lie immediately in front of the 

 anterior roots of the spinal accessory nerve, and in line with 

 them. They arise from groups of neuroblasts in the walls of the 

 medulla oblongata (Fig. 228), in a manner precisely similar to 

 that in which the ventral spinal roots are formed. The nerve 

 fibres converge to form small bundles which leave the medulla 

 immediately ventral to the much larger and more conspicuous 

 sensory root (Fig. 228, x.s), by which they are covered and 

 more or less completely concealed. 



The motor roots of the glossopharyngeal, or ninth cranial nerve. 

 are exactly similar to those of the pneumogastric ; they lie im- 

 mediately in front of these, and in line with them, and in trans- 

 verse sections present an appearance practically identical with 

 that shown for the pneumogastric nerve in Fig. 228, X.m. 



The facial, or seventh cranial nerve (Fig. 227, vn), arises 

 from a group of neuroblasts in the side wall of the medulla 

 oblongata, opposite the auditory vesicle. The bundle of axis 

 cylinders, formed as outgrowths of the neuroblasts, does not at 

 once pass out from the medulla, but runs forwards a short 

 distance in its substance, and emerges immediately below the 

 auditory nerve and in very close relation with this. The root of 

 the facial nerve lies in line with the motor roots of the glosso- 

 pharyngeal and pneumogastric nerves, i.e. it belongs to the 

 lateral series of motor roots. 



The chorda tympani is present early in the fifth week as an 

 .ulterior branch of the facial nerve, which runs in the tympanic 

 membrane, but does not yet reach the trigeminal nerve. 



The sixth cranial nerve belongs to the ventral series of motor 

 roots. It arises from several groups of neuroblasts which lie in 

 the ventro-lateral area of the medulla oblongata, in line with 

 the hypoglossal roots, and vertically below the root of the 

 auditory nerve, i.e. a short distance anterior to the root of the 

 facial nerve. The sixth nerve, after emerging from the brain. 



