ORIGIN OF CRANIAL NERVES. 181 



round, and smaller than the auditory, internal to which it is placed. It 

 issues from the lateral tract of the medulla at the upper part, and is con- 

 nected by a slip with the lower border of the pons. 



The facial nerve receives a small accessory band of fibres (intermediate 

 portion of Wrisberg) from the same part of the medulla, and enters the 

 internal meatus with the auditory trunk. 



The auditory nerve (portio mollis, eighth nerve, Sommerring) has a 

 surface attachment to the restiform body and the floor of the fourth ven- 

 tricle. The nerve is very soft, and receives one of its names from that 

 fact. 



Deep origin. The facial nerve penetrates to the floor of the fourth ventricle, and 

 arises from the same nucleus as the sixth nerve, which it joins (Clarke 1 ). 



The fasciculus of the auditory nerve which reaches the floor of the fourth ventri- 

 cle, bends backwards over the restiform body to the auditory nucleus ; and some 

 arciform fibres out of the median sulcus are joined with this part of the root. 

 The other fasciculus pierces the restiform body, and takes origin from a network 

 connected with the posterior pyramid (Clarke). 



The EIGHTH CRANIAL NERVE (Willis) ( 8 ) is placed along the side of 

 the medulla oblongata, and consists of three distinct trunks, glosso- 

 pharyngeal, pneumogastric, and spinal accessory : the names of the first 

 two indicate their destination ; and the last, besides being accessory to the 

 pneumogastric, supplies some muscles. 



The glosso-pharyngeal nerve (ninth nerve, Sommerring) is the smallest 

 of the three, and is situate highest. Its apparent origin is by three or 

 more fibrils, which penetrate the lateral tract of the medulla close to the 

 facial nerve. 



The pneumogastric or vagus (tenth nerve, Sommerring) is connected 

 with the lateral tract of the medulla, below the glosso-pharyngeal nerve, 

 by a series of filaments, which are collected at first into bundles, but are 

 finally gathered into one flat band. 



The spinal accessory nerve (eleventh nerve, Sommerring) consists of 

 two parts accessory to the vagus, and spinal. 



The accessory part is of small size, and arises by fine filaments in a line 

 with the root of the vagus, as low as the first cervical nerve. Finally this 

 fasciculus throws itself into the pneumogastric nerve outside the skull. 

 (See p. 114.) 



The spinal part is firm and round, like the third or the sixth nerve, but 

 only a small piece of it can be seen. It arises by a number of fine fila- 

 ments from the lateral column of the spinal cord near the lateral fissure, 

 as low as the sixth cervical nerve. As the nerve ascends along the side 

 of the cord it lies between the ligamentum denticulatum and the posterior 

 roots of the spinal nerves, with the upper of which it may be connected ; 

 and it finally enters the skull by the foramen magnum. 



All three nerves converge below the crus cerebelli, and rest on a small 

 lobe of the cerebellum (flocculus). From that spot they are directed out- 

 wards to the foramen jugulare (p. 32). 



The fibrils of the nerves pierce the medulla ; and each nerve, except the 

 spinal part of the last, takes origin from a special deposit of gray matter at 

 the back of the medulla oblongata, and near the lower of the fourth ven- 

 tricle (p. 217). 



' On the structure of the Medulla Oblongata, by J. Lockhart Clarke, F. R. S., in 

 the Philosophical Transactions for 1858, part i. 



