14 . GRAY SUBSTANCE OF THE MEDULLA OBLONGATA. 



Intermingled with the large multipolar cells are others presenting every variety 

 of form and size, obovate, stellate, and fusiform. 



The larger cells measure on an average in their longest diameter, in the sheep 

 ^i_ to g-J-o of an inch. In the cat y 2V0 ^^ j'k's ^^ ^^ inch. In the human medulla 

 ToVo to eh of an inch. 



These cells are collected into groups more or less distinct according to the region 

 in Avhicli they are observed, and are also connected by their processes in the same 

 manner as I have shown to be the case in the anterior cornua of the spinal cord, 

 though from the cells being so closely crowded together, the connections are very 

 difficult to trace satisfactorily. * 



The cell processes are sent out in various directions, both longitudinal and trans- 

 verse, their general course having been already described by Clarke.^ Some of them 

 go upwards to cells of the same nucleus, some run backwards and enter the neighbor- 

 ing spinal accessory, or vagal nuclei, or are continuous with the roots of these nerves ; 

 a third set decussate at the raphe, and are either continuous with its fibres, or 

 cross over into the opposite nucleus, the two nuclei being thus brought into close 

 connection; whilst a fourth set pass out into the network by which the nucleus is 

 bounded anteriorly and antero-lateraUy, the network itself containing, as mentioned 

 above, very numerous cells of difi'erent form and size. Many of the cell processes, 

 especially those from the anterior part of the nucleus, are continuous with the 

 hypoglossal roots. 



The courses pursued by these cell processes will be seen at a glance to be strictly 

 analogous with the general direction which the cell processes foUow in the anterior 

 cornua of the spinal cord. 



The connection between the hypoglossal nuclei and olivary bodies, by direct 

 fibres and by numerous little cell groups scattered along the raphe and hypoglossal 

 roots, will be noticed in describing the olivary bodies and their accessory nuclei. 



The Hoots. — In man the hypoglossal roots enter between the olivary column and 

 the anterior pyramid (Plate VII, Figs. 26, 26, 27), penetrating the olivary body in 

 the upper part of the medulla in a serpentme course (Fig. 27), but never, so far as I 

 have been able to ascertain, entering into any immediate connection either with 

 the cells or fibres of the olivaries. 



In most of the mammalia the plan is somewhat diffierent, owing to the greatly 

 diminished size of the pyramids and olivary bodies, the latter being situated behind 

 the pyramids on each side of the raphe, allowing the hypoglossal roots to pass 

 outside of them (Plates I, II, and XIII). 



The hypoglossal roots in man, after curving around the border of the olivary 

 bodies, or penetrating them in one or more bundles, pursue a direct course to the 

 nucleus, the apex of which they enter ; in the mammalia the course is the same, 

 with the single exception that they pass along the outer edge of the olivaries, and 

 only penetrate among the scattering cells near the extreme outer edge. 



On reaching the nucleus the greater part of the fibres proceed directly inwards, 

 as do those of the anterior spinal roots, becoming connected Avith the large groups 



' Philos. Trans. 1858 



