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Leonardo da Vinci (1452-1519)

Recto: The brachial plexus. Verso: The brachial plexus and nerves of the arm c. 1508

Pen and ink over black chalk | 19.1 x 13.7 cm (sheet of paper) | RCIN 919040

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  • A folio from Leonardo's 'Anatomical Manuscript B'.

    On the recto: two diagrammatic drawings of the neck and upper thorax showing the origins of the brachial plexus of nerves; the coverings of the spinal cord and the roots of the nerves; notes on the drawings.

    The two principal drawings here must be taken together with those on either side of RCIN 919021, which together constitute a sequence of schematic diagrams of the brachial plexus (see also 919020v. In the first, on 919021v, the seven cervical and first two thoracic vertebrae are shown together with the clavicles and first two pairs of ribs, a gap where the sternum would be, and the brachial plexus on either side of the vertebrae formed from spinal verves. In the second diagram, on the present sheet, the vertebrae are sectioned longitudinally to reveal the spinal cord with two parallel ancillary structures within the body of the vertebrae. The third diagram, immediately below, depicts this arrangement of nerves in isolation, with the base of the brain included; and the fourth diagram, on 919021r, shows the bones alone, with the cavities supposed to house these nerves. On 919021v Leonardo also gives two details of the spinal cord and ancillary structures entering the brain, and at upper right on the present sheet, a diagram of the membranous nature of the spinal cord.

    Though the schematic nature of these diagrams might suggest that they are final expressions of Leonardo’s understanding of the brachial plexus, they are in fact less accurate than the more loosely drawn 919020v. Four spinal nerve roots are shown rather than the correct five, and the pattern of branching in the plexus is excessively simplified. The structures either side of the spinal cord are presumably intended to be the sympathetic trunks, a pair of bundles of nerve fibres and ganglia that run parallel to the spinal cord, from which nerves issue that pass both into the spinal nerves and through the foramina (holes) of the transverse processes of the cervical vertebrae. From the superior ganglion of the trunk, nerves arise and pass into the cranium via the carotid canal, accompanying the internal carotid arteries, but the sympathetic trunks themselves do not enter the cranium. The sympathetic trunks lie anterior to the transverse processes and do not play a significant role in the formation of the brachial plexus; the structures which present in this manner, passing through the body of the cervical vertebrae, are in fact the vertebral veins and arteries. The appearance of the sympathetic trunk changes greatly as it goes from the thorax into the neck: in the thorax it is quite regular, with ganglia and communicating rami at each level, but above the first rib it has only three or so ganglia and can be of much smaller diameter. Leonardo may well have been confused by this transition: even with modern dissection methods, and knowing what to expect, this can be a very difficult area.

    On the verso: three studies of the right arm, drawn to show the nerves; notes on the drawing and a list of examples to be presented. The drawings again illustrate the nerves of the brachial plexus and right arm, here seen from the back with the arm held out, and can best be understood by turning the sheet anticlockwise. They attempt to show the innervations of the muscles by specific nerves; that on the right labels four of the muscle masses as ‘shoulder’ (deltoid), ‘humerus’ (probably brachialis), ‘fish of the arm’ (biceps) and ‘muscle of the elbow’ (triceps). Leonardo believed that nerves ramified within the body of the muscle, ensheathing each muscle fibre individually and causing it to contract when stimulated (see the passage on the recto. The brachial plexus is shown with only four roots, and not the correct five. In the drawing to the left the distribution of ulnar and radial nerves on the hand is reliable – this represents quite a feat of dissection.

    The lower part of the sheet is filled with one of Leonardo’s programmes for his intended treatise. Compared with earlier programmes (eg. on 919059v) it is notable that the emphasis is here entirely anatomical, with no overt concern for the phenomena of life. His word dimosstratione emphasises the didactic nature of the treatise. The list is a little confused by Leonardo’s indiscriminate use of nervi to mean nerves, tendons or ligaments; it is left untranslated below unless the meaning is clear from the context.
    A demonstration of the omentum without the intestines
    A demonstration of the bones, sawn
    A demonstration of the bones, whole
    A demonstration of the bones and nervi
    A demonstration of the bones and veins
    A demonstration of the nervi and muscles
    A demonstration of the veins and muscles
    A demonstration of the bones and intestines
    A demonstration of the mesentery and muscles
    A demonstration of the spiritual parts [thoracic organs]
    A demonstration of the female
    A demonstration of the bones, nerves and veins
    A demonstration of the nerves alone [cf. 919034v]
    A demonstration of the bones alone
    A demonstration of the tendons on bones, sawn
    A demonstration of the tendons on bones, whole
    A demonstration of the bones and ligaments which join each other together, which ligaments are very short, particularly those that join the vertebrae.

    Text adapted from M. Clayton and R. Philo, Leonardo da Vinci: Anatomist, London 2012
    Provenance

    Bequeathed to Francesco Melzi; from whose heirs purchased by Pompeo Leoni, c.1582-90; Thomas Howard, 14th Earl of Arundel, by 1630; Probably acquired by Charles II; Royal Collection by 1690

  • Medium and techniques

    Pen and ink over black chalk

    Measurements

    19.1 x 13.7 cm (sheet of paper)


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