HUMAN AND MAMMALIAN. 



21 



larger nucleus of the upper roots of the spinal accessory, the nucleus of which con- 

 tinually increases in size as we ascend towards the vagus/ 



In man I have usually been able to trace the continuity of these columns 

 into the medulla. The cells of the posterior vesicular columns are often very 

 much scattered, but rarely if ever disappear, and although the nucleus of the 

 accessory, between the first cervical and lowest roots of the hj'poglossal, is princi- 

 pally formed from the tractus intermedio-lateralis, it is constantly imited to and 

 reinforced by cells from the vesicular column. (Fig. 5.) In the upper part of the 



Fig. 5. 



Posterior cornu from the human medulla. — a, Nucleus of the spinal accessory ; 6, caput cornu ; c, central canal 

 d, restiform nucleus ; /, tractus intermedio-lateralis ; p, post-pyramidal nucleus. 



spinal accessory nucleus and still more distinctly in that of the vagus, it will be 

 noticed that the nucleus is composed of two distinct cell groups, one anterior, derived 

 chieily from the tractus intermedio-lateralis, this group apparently serving to receive 

 the anterior roots of these nerves, and to unite them with the hypoglossal nucleus ; 

 "the other posterior, derived from the posterior vesicular columns, receiving the pos- 

 terior roots, and united by means of cells with the post-pyramidal and restiform 

 nuclei, which are entirely derived, as we have seen, from the posterior vesicular 

 columns. It wUl thus be seen that in the medulla, cell groups are formed, which 

 if not direct continuations of the posterior vesicular columns and tractus intermedio- 

 lateralis, are doubtless connected with them, and may certainly be considered as 

 representing them, bearing the same relation to the posterior nerves of the medulla 

 which these columns have been shown to sustain to the posterior spinal roots in the 

 cord. These columns, moreover, though not always so compact and weU defined 

 as they are seen to be in the region of the accessory and vagus, may nevertheless 

 be traced continuously throughout the medulla in close connection with the spinal 

 accessory, vagus and glosso-pharyngeal nerves, as well as a part of the auditory and 

 trifacial roots. 



* In the sheep the nucleus of the spinal accessory seems to be formed more exclusively Irom the 

 tractus intermedio-lateralis, than it is in the human medulla or in that of the cat. 



