658 THE GREY MATTER OF THE MEDULLA OBLONGATA. 



fibres through it, so that it forms a forraatio reticularis, separating the two eomua (tig. 465, fr)- 

 The caput cornu iwsterioris conies to be covered higher up by the ascending root of the 5th 

 nerve (tig 465 aV), and arcuate fibres losing to the restiforin body, lhe posterior cornu is 

 also broken up and is thrown outwards, its caput giving rise to part of the elevation seen on the 

 surface and described as the funiculus of Rolando, while part of the base now greatly enlarged 

 tonus the grey matter in the funiculus gracilis [clavate nucleus] (tig. 464, ng) and funiculus 

 cuueatus [cuueate or triangular nucleus] (tig. 464, nc). Nearer the middle line, the grey matter 

 of the posterior grey cornu appears in the ttoor of the 4th ventricle, above the point where the 

 central canal opens into it, as the nuclei of the spinal accessory, vagus, and glossopharyngeal 



ne fln > tlie floor of the 4th ventricle near the raphe, and quite superficial, is a longitudinal mass 

 of large multii>olar nerve-cells, derived from the base of the anterior cornu from which spring 

 the several bundles forming the hypoglossal nerve ; it is the hypoglossal nucleus (fig. 466, nXIl), 

 tl.- nerve-fibres passing obliquely outwards to appear between the anterior pyramid and the 

 olivarv body. Internal to it, and next the median groove, is a small mass of cells continuous 

 with those in the raphe, and called the nucleus of the funiculus teres (fig. 466, id). Around 

 the central canal at the lower part of the medulla is a group of cells (tig. 466, nXl), which 

 becomes displaced laterally as it conies nearer the surface in the floor of the medulla oblongata, 

 where it lies outside the hypoglossal nucleus, and corresponds to the prominence of the ala 

 ciuerea fig. 4o6, nX) ; and from it and its continuation upwards arise from below upwards part 

 of the spinal accessory (11th), and the vagus (10th, corresponding to the position of the 

 eminentia cinerea -fig. 466, A'), so that this column of cells forms the vago-accessorius 

 nucleus. External to and in front of this is the nucleus for the glossopharyngeal nerve. 

 Further up in the medulla, 011 a level with the auditory striae and outside the previous column, 

 is a tract of cells from which the auditory nerve (8th) in great part arises ; it is the principal 

 auditory nucleus, and lies just under the commencement of the inferior cerebellar peduncle 

 fig. 427, 8', 8", 8'"). It consists of an outer and inner nucleus, which extend to the middle line. 

 It forms connections with the cerebellum, and some fibres are said to enter the inferior cerebellar 

 peduncle. This is an important relationship, as we know that the vestibular branch of the 

 auditory nerve conies partly from the semicircular canals, so that in this way these organs may 

 be connected with the cerebellum.] 



[Superadded Grey Matter. There is a superadded mass of grey matter not represented in 

 tlu- cord, that of the olivary body, enclosing a nucleus, the corpus dentatum, with its wavy 

 strip of grey matter containing many small multipolar nerve-cells embedded in neuroglia. The 

 grey matter is covered on the surface by longitudinal and transverse tibres. It is open towards 

 the middle line (hilum), and into it run white fibres forming its peduncle (fig. 466, p, 0, I). 

 These tibres diverge like a fan, some of them ending in connection with the small multipolar 

 cells of the dentate body, while others traverse the lamina of grey matter and pass backwards 

 to appear as arcuate fibres which join the restiforin body ; others, again, pass directly through 

 to the surface of the olivary body, which they help to cover as the superficial arcuate fibres. 

 The accessory olivary nuclei (fig. 465, 0', 0") are two small masses of grey matter similar to the 

 last, and looking as if they were detached from it, one lying above and external, sometimes 

 called the parolivary body, and the other slightly below and internal to the olivary nucleus, 

 the latter being separated from the dentate body by the roots of the hypoglossal nerve. The 

 latter is sometimes called the internal parolivary body, or nucleus of the pyramid.] 



[The formatio reticularis occupies the greater part of the central and lateral parts of the 

 medulla, and is produced by the intercrossing of bundles of fibres running longitudinally and 

 more or less transversely in the medulla (fig. 465, fr). In the more lateral portions are large 

 multipolar nerve-cells, perhaps continued upwards from part of the anterior cornu, while the 

 part next the raphe has no such cells. The longitudinal fibres consist of the upward prolonga- 

 tion of the antero-external columns of the cord, while some seem to arise from the clavate nuclei 

 and olives as arcuate fibres passing upwards. In the lateral portions, the longitudinal fibres 

 are the direct continuation upwards of Flechsig's antero-lateral mixed tracts of the lateral 

 columns (p. 633). The horizontal fibres are formed by arcuate fibres, some of which run more 

 or less transversely outwards from the raphe. The superficial arcuate fibres (fig. 466, /, a, e) 

 appear in the anterior median fissure, and perhaps come through the raphe from the opposite 

 side of the medulla, curve round the anterior pyramids, form a kind of capsule for the olives, 

 and join the restiform body (p. 656), but they are reinforced by some of the deep arcuate fibres 

 which traverse the olivary body (p. 656). The deep arcuate fibres run from the clavate and 

 triangular nuclei horizontally inwards to the raphe, and cross to the other side ; others pass 

 from the raphe to the olivary body, and through it to the restiform body. In the raphe, 

 which contains nerve-cells, some tibres run transversely, others longitudinally, and others from 

 before backwards.] 



[Other Nerve Nuclei Sixth Nerve. Under the elevation called eminentia teres (fig. 427) 

 in front of the auditory strhe, close to the middle lino, is a tract of large multipolar nerve-cells. 

 It was ouce thought to be the common nucleus of the 6th and 7th facial nerves, but Gowers 

 has shown that " the facial ascends to this nucleus, forms a loop round it (some fibres indeed 



