Recto: an anatomical drawing of a neck, showing the muscles, veins, cartilage of the throat and part of the spine; a skull, turned in profile to the left; an outline of a head; a neck; a man's face in profile to the right. Verso: an apse of a church, with an arcade of windows and a semi-dome, like a shell, showing also the square end of the left aisle; the word cori in a 16th-century hand.

The principal drawing on the recto depicts a variety of structures in the neck. The hyoid bone and laryngeal apparatus are not human, and the proportions of the smaller study to centre right – faded, and visible only in ultraviolet light – suggest that a monkey was Leonardo’s subject. Such is the density of detail that Leonardo provided key letters on the clavicle, though it is not always clear which structures these letters refer to. Prominent are the diagonal sternocleidomastoid muscle (M) and the external jugular vein (P), with its branches outlined in pen in the smaller study to the right. R S T are at approximately the positions where the internal jugular vein, common carotid artery and vagus nerve pass behind the clavicle (collarbone). A portion of the temporalis muscle is seen passing deep to the zygomatic arch (cheekbone), and at the back of the neck there is an odd depiction of what might be the trapezius muscle reduced to two ‘strings’ to show the deeper muscles such as splenius.

In the delicate metalpoint sketch to the left, temporalis is seen again, and Leonardo has indicated the zygomaticus major muscle and part of the complex of levator muscles which lift the upper lip.

To lower right is a head and neck of a type drawn habitually by Leonardo. The sternocleidomastoid muscle is again prominent, though Leonardo has depicted it travelling backwards to the shoulder, rather than forwards to the clavicle and sternum. At lower left is what may be a first attempt to understand the oblique muscles of the anterior abdominal wall, shown travelling between the iliac crests and the opposite lower ribs and thus crossing the midline of the body, which they do not do.

Text adapted from M. Clayton and R. Philo, Leonardo da Vinci: Anatomist, London 2012, no. 4