586 THE CRANIAL NERVES. 



3. The third pair of nerves (motores oculorum) have their apparent or 

 superficial origin from the inner surface of the crura cerebri in the inter- 

 peduncular space, immediately in front of the pons. Each nerve consists 

 of a number of funiculi which arise in an oblique line from the surface. 



The deeper fibres of origin, when followed into the cms, are found to diverge 

 in its substance, some being traced to the locus niger, others running down- 

 wards in the pons among its longitudinal fibres, and others turning upwards to be 

 connected with the corpora quadrigemina and Vieussenian valve. According to 

 Stilling, with whom Kolliker agrees, the major part of the fibres arise from a grey 

 nucleus in the floor of the Sylvian aqueduct, close to the origin of some fibres of the 

 fourth nerve. 



4. The fourth pair, pathetic or trochlear nerves, the smallest of those 

 which are derived from the brain, are seen at the outer side of the crura 

 cerebri immediately before the pons. Each nerve may be traced backwards 

 round the peduncle to a place below the corpora quadrigemina, where it arises 

 from the upper part of the valve of Vieussens. Kolliker states that, under 

 the corpora quadrigemina, the fibres of origin are divided into two bundles ; 

 the anterior being traceable through the lateral wall of the aqueduct of 

 Sylvius to its floor, where it arises from a grey nucleus close to the middle 

 line ; the posterior bundle being derived from a grey nucleus in the floor of 

 the fourth ventricle, close to the origin of the fifth nerve. The roots of the 

 nerves of opposite sides are connected together across the middle line in the 

 form of a white band or commissure in the substance of the velum. 



5. The fifth pair of nerves, par trigeminum, trifacial nerves, take their 

 superficial origin from the side of the pons Varolii, where the transverse 

 fibres of the latter are prolonged into the middle crus cerebelli, considerably 

 nearer to the upper than to the lower border of the pons. 



The fifth nerve consists of a larger or sensory, and a smaller or motor 

 root. The smaller root is at first concealed by the larger, and is placed a 

 little higher up, there being often two or three cross fibres of the pons 

 between them. On separating the two roots, the lesser one is seen to 

 consist of a very few funiculi. In the larger root the funiculi are numerous, 

 amounting sometimes to nearly a hundred. 



Deep origin. The greater root runs behind the transverse fibres of the pons towards 

 the lateral part of the medulla oblongata at the back of the olivary body. Several 

 anatomists trace it into the floor of the fourth ventricle, between the fasciculi teretes 

 and the restiform bodies. By some it is considered to be continuous with the fasci- 

 culi teretes and lateral columns of the cord, whilst others connect it with the grey 

 mass which is regarded by Stilling as the nucleus of the glosso-pharyngeal nerve. 



The motor root was supposed by Bell to descend to the pyramidal body, and 

 Retzius believes that he has confirmed that opinion by dissection : but it would 

 appear that the deep connection of this root is not yet known with certainty. 

 According to Stilling the fibres pass through the pons to the floor of the fourth 

 ventricle, and have their origin in its grey matter. 



According to Foville, some of the fibres of the sensory root of the fifth nerve are 

 connected with transverse fibres in the pons, whilst others spread out on the surface 

 of the middle peduncle of the cerebellum, and enter that part of the encephalon 

 beneath the folia. (Op. cit. p. 506.) 



6. The sixth nerve (abducens), motor oculi externus, takes its apparent 

 origin from between the pyramidal body and the pons Varolii by means 

 of a larger and a smaller bundle. It is connected with the pyramid, and to 

 a small extent with the pons also. Philipeaux and Vulpian, with whom 



