386 ORIGINAL ARTICLES. 



the lateral white column. From the upper part of the lumbar to 

 the lower part of the cervical regions of the cord, the lateral portion 

 of the grey substance between the anterior and posterior cornua con- 

 sists of a peculiar vesicular tract, paler and more transparent than 

 the rest, and which has been named by Lockhart Clarke the tractus 

 mtermedio-lateralis. (Plate X. figs. 3 and 4.) This tract consists, for 

 the most part, of oval, fusiform, and pyi'iform cells sending processes 

 to the lateral columns and to the transverse commissures. The tractus 

 mtermedio-lateralis was first shown by Mr. Clarke, to be in intimate 

 connection with the lower roots of the spinal accessory nerve in the 

 cervical region. It constitutes the motor column of the respiratory 

 muscles of the abdomen and thorax. 



" The tractus intermedio-lateralis, in Man, closely resembles that 

 of Mammalia, and contains cells of the same kind, but rather smaller. 

 In the upper part of the cervical region, a similar, but somewhat 

 larger, tract reappears in the same situation, and projects in the same 

 way into the lateral column. It increases in ascending to the third 

 pair of nerves, where the form of the entire grey substance presents 

 a very striking resemblance to that in the upper part of the dorsal 

 region. This tract is traversed by several roots of the spinal acces- 

 sory nerve, in their course forwards to the anterior cornu, and con- 

 tributes, with the edge of the posterior cornu, to form a beautiful 

 network in the lateral column, through which the nerve enters. Its 

 cells are triangular, oval, and fusiform in different directions : some 

 of them are elongated in the direction of the transverse commissure, 

 and towards the front of the posterior vesicular column ; others ex- 

 tend outwards with radiating fibres through fissures of the lateral 

 column. Tliere is reason, therefore, to believe that this tract forms 

 a part of the tractus intermedio-lateralis. In the Sheep and Ox, and 

 probably in all Mammalia, a peculiar group of cells, which is tra- 

 versed by the roots of the spinal accessory nerve, is found in the 

 same situation ; and this group, in ascending the medulla oblongata, 

 retires inwards to the s])ace behind the canal, and there contributes 

 to form the nucleus which gives origin to the highest roots of the 

 nerve. The cells ol» the tractus intermedio-lateralis are elongated 

 with their processes in a longitudinal direction, and reached by both 

 the posterior and anterior roots of the spinal oierves, and perhaj)s by 

 the spinal-accessory. ■ The latter nerve extends fonoards to the ceUs 

 of the anterior cornu, which also send some of their processes longi- 

 tudinally, and are reached by the posterior roots. 



Mr. Clarke has shown that while one portion of the upper roots 

 of the spinal-accessory nerve, and one portion of the vagus roots pro- 

 ceed inwards to their respective nuclei beJiind tJie canal, other portions 

 of both bend forwards to the vesicular network into which the anterior 

 cornu has become resolved, and that some of the roots of the trifacial 

 nerve descend lonyitvdinaUy throvr/h the caput eornio, between the 

 transverse roots of the vagus. In this course they are probably 

 brought into connexion with the respiratory centres, and perhajjs also, 



