The latter two are innervated by the suprascapula nerve. The coracobrachalis pre-muscle mass is associated with biceps . Likewise, three heads are beginning to appear on triceps and the muscle is part of a mass innervated by the radial nerve. Brachialis is innervated by the musculocutaneous nerve and possesses fibres. It is inserted into the ulna.
Supinator is described as arising in conjunction with the extensor mass .
It was identified by the direction of fibres and position. A superficial extensor muscle mass, supplied by branches of the posterior interosseus nerve, probably represents the future extensor digitorum, extensor carpi ulnaris and extensor digiti minimi . Rectus abdominis is mentioned as a mass situated more ventrally. Plate V Fig. 43 in great detail.