HUMAN AND MAMMALIAN. . 13 



CHAPTER III. 



THE HYPOGLOSSAL NUCLEUS AND ROOTS. 



The Nucleus. — StiUing^ Avas the first to point out the true origin of the hypoglos- 

 sal roots, from the two groups of nerve cells which make their appearance just above 

 the upper cervical nerves, in front of the central canal, extending laterally to a con- 

 siderable distance on each side. These groups seem to be a continuation of the 

 cell colunms from which the anterior spinal roots arise, being situated within what 

 is evidently the posterior portion of the anterior cornua, the anterior portion of which 

 has already been broken up into an open network by the passage of numerous 

 longitudmal fasciculi, to such an extent that the portion in the immediate vicinity 

 of the central canal, together with a branching wing on each side the raphe, alone 

 remains distinct. 



The form of the hypoglossal nucleus as it appears just above the decussation of 

 the pyramids, is nearly pyramidal, with its apex directed forwards towards the roots, 

 varying but slightly in those mammalia I have examined, from its shape ia man, 

 the only difierence arising from the greater general concentration of structure in 

 the human medulla. These slight differences wUl be readily seen by comparing 

 Figs. 17, 18, 19, 20, 21, 22, Plates V and VI, from the human meduUa, with the 

 corresponding sections from the sheep. Plates I, II, Figs. 1, 2, 3, 4, 5, 6. 



Higher up the nucleus increases somewhat in size, and is gradually pushed 

 slightly backwards and outwards, changing its form someAvhat, becoming almost 

 square close to the calamus scriptorius (Plates I, II, Figs. 4, 5 ; Plate VI, Fig. 21), 

 and having attained its greatest development, gradually diminishes in size, reassum- 

 ing presently its former pyramidal shape, finally becoming covered over by the 

 auditory ganglion. Fig. 7, Plate II, shows the last remains of the hypoglossal which 

 in Fig. 8 is completely merged in the auditory nucleus. 



The oval ceU groups which occupy abeady a large portion of the nucleus on each 

 side of the middle Hne, increase rapidly in size and number of cells as they ascend, 

 until their point of greatest development is reached a little above the calamus 

 scriptorius. 



The cells are mostly quite large, steUate or oblong in shape, and multipolar, 

 resembling in every respect those found in the anterior cornua of the spinal cord, for 

 which they might easily be mistaken.^ 



' Medulla Oblongata. Erlangen, 1843. 



° The great similarity both in the form of the cells and the general relations which these bear to 

 the roots may be seen by comparing one of the figures from my memoir on the spinal cord (Memoirs 

 of the American Academy, 1861, fig. 4), with pi. x, fig. 37 of the present memoir, the principal dif- 

 ference being solely that the cells of the hypoglossal nucleus are much more closely crowded together 



