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FOURTEEN FIGURESThe purpose of this investigation was to localize the columns of cells which give rise to the motor components of the nerves of the brachial plexus in Macaca mulatta. I n addition, as a basis for the experimental work, it was found advisable to describe briefly the arrangements of the cell groups of the cervical and first thoracic segments. MATERIAL AND METFI0I)SThe experimental animals used were nine Macaca mulatta monkeys. With the exception of one adult female they were immature specimens. Their average weight was about 2.25 kg. The operations on these animals were done under aseptic conditions. Excepting one case, the nerves were approached and cut in the axilla. The incision for the suprascapular nerve was made along the lateral border of the trapezius muscle. I n each animal the nerve to be cut was isolated from the surrounding tissues, care being taken not to disturb other nerves or to traumatize adjacent muscles. A piece about 2.5 cm. long was excised from the isolated nerve. The overlying layers of tissue were then sutured and the incision bandaged.Following the procedure of Papez ('27) the animals were killed 13 to 17 days after the operation. The spinal cords were immediately removed and placed in trichloracetic solution (Huber, '27) for fixation. Autopsies mere done in every case to determine the distribution of the excised nerves.

THE GROUP OF SYMPTOMS commonly referred to as the scalenus anticus syndrome seems more likely to develop in certain persons than in others. Bilateral dissections of the area in question were done on 56 cadavers in an effort to discover significant anatomic relations to explain this fact. Particular attention was directed toward the modifications in structure and anatomic relations of the scalene muscles, the components of the brachial plexus and the adjacent vessels.It should be recalled that originally this set of symptoms was associated only with the presence of a cervical rib and was designated as the syndrome of the cervical rib. Subsequent investigations further clarified the problem and demonstrated that other factors entered into the production of the syndrome. The syndrome of the cervical rib was described by Murphy1 as including any or all the following: 1) pressure on the trunks of the brachial plexus with pain, paresthesia, hypesthesia, or anesthesia in the peripheral area of distribution of the involved sensory fibers, and paresis or paralysis of the muscles supplied by the involved motor fibers, 2) pressure on the subclavian artery with brachial ischemia and possible aneurysmal formation, thrombosis and gangrene, and 3) development of a tumor in the supraclavicular triangle. The fact that this syndrome might occur in the absence of a bony anomaly was recognized by Murphy,2 who described a case which presented many of the manifestations of the cervical rib syndrome but no cervical rib was present. At operation the lower trunk of the brachial plexus was found on the inferior portion of the anterolateral border of the scalenus medius muscle. The insertion of the muscle at that point was severed and the subjacent portion of the rib resected. There was complete relief of symptoms. Jones3 stated that in some individuals the eighth cervical and first thoracic segments contribute an unusually large proportion of the fibers to the brachial plexus and in these cases the first thoracic rib may traumatize the lower trunk of the plexus. Post-fixation of the brachial plexus was the term applied to those cases in which a comparatively large number of the component fibers emerge through the lower contributing segments. A plexus which received a relatively large number of fibers from the upper contributing segments was termed pre-fixed. Wilson4 described two main types of muscular involvement by cervical ribs. One was designated the median type because some or all the 1182

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