LTHOUGH thyroid operations are A performed by genera1 surgeons, their compIications are seen by the Iaryngologist. Most of these comphcations are due to damage to the nerves which occurs during the operation, and cause anxious moments for the operator who does not have a clear conception of what changes take pIace in the larynx. My aim is to cIarify this picture and show the changes that wiI1 be encountered if one or more Iaryngeal nerve is affected. The symptoms foIIowing these injuries are manifoId, but they can be divided into two main groups: first, changes in the voice; second, changes in the breathing. There are other symptoms such as spasmodic cough, difhcuIty in deglutition, and inabiIity to cIear the Iarynx of mucus. To be able to expIain what takes place, it is necessary to discuss the normaI innervation of the Iarynx and its physioIogy. (Figs. I and 2.) Some controversy stiI1 exists over the reIationship of the IaryngeaI nerve to the thyroid gIand, and aIso over the innervation of the Iarynx itseIf. It is known that the Iarynx is suppIied by two nerve trunks which originate in the vagus: (I) the Iaryngeal inferior, or recurrent nerve which suppIies a11 the IaryngeaI muscIes with motor fibers except the cricothyroid muscIe; (2) the IaryngeaI superior nerve which carries sensory fibers in the strong externa1 portion to the Iarynx, and motor fibers in the weaker internal portion to the cricothyroid. The schematic picture (Fig. 3), the work of Professor Onodi, who did the pioneer work on the nerve suppIy of the larynx, is stiI1 accepted by most Iaryngologists. It is evident from Onodi’s picture that besides the two main nerve trunks, the Iowest branch of the IaryngeaI superior nerve is connected with the media1 branch of the inferior nerve under the mucosa which covers the crico-arytenoid posterior muscIe, forming the so-caIIed ansa GaIeni. Both nerves have connections with the sympathetic nerves. Besides these cIear cut cases there are many irregmarities of innervation or overIapping innervation. The recurrent nerve may send some motor Iibers to the abductors, adductors and tensors. The compIexity of this innervation is evident from the different, and by no means cIearIy expIainabIe, Iaryngeal conditions which are found when these cases are folIowed up, and which cannot be interpreted as injury to only one specific nerve. The most important structure which is frequentIy affected by the nerve injuries is the crico-arytenoideus posterior, also caIIed the posticus or abductor muscle, innervated by the IaryngeaI inferior or recurrent nerve. Second in importance is the interarytenoid muscIe. WhiIe the innervation of the abductor is cIear cut, there is considerabIe difference of opinion regarding the nerve suppIy of the interarytenoid muscle. Heyd,’ quoting Frazier,2 states that the interarytenoid muscIe is supplied by the internal branch of the superior IaryngeaI nerve, whiIe ZiegeIman” cIaims that a combination of recurrent and superior nerves is