PAR VAGUM. 



895 



has published various experiments upon these 

 nerves very similar to those which we had per- 

 formed, and obtained nearly the same results. 

 Longet states that the respirations become in- 

 creased in frequency after dividing the recur- 

 rents. Other experimenters have lately satisfied 

 themselves of the accuracy of these experiments. 



Effects of the laryngeal nerves on phonation. 

 The effect of the lesion of the recurrent 

 nerves in enfeebling the voice was well known 

 to Galen and the older physiologists.* We 

 found in making this experiment that the voice, 

 as Monro Secundusf and others have stated, 

 is not altogether lost, for in some cases, at 

 least, the animal could still emit a faint howl. 

 Longet | has observed that the voice is com- 

 pletely lost in old animals, while young animals 

 are still able to produce acute sounds different 

 from the natural voice if the cri co-thyroid 

 muscle moved through the external branch of 

 the superior laryngeal be not paralysed, and he 

 attributes this difference to the relative size of 

 the larynx at these ages. We can have no 

 doubts in attributing the effects of lesion of the 

 inferior laryngeals upon the voice to the para- 

 lysis of the muscles attached to the arytenoid 

 cartilages. 



Magendie mentions that an animal after 

 section of the superior laryngeal nerves " loses 

 almost all its acute sounds it acquires, besides 

 a constant gravity which it had not previously. "|| 

 This he attributed to the arrestment of the 

 movements of the arytenoid muscles, but we 

 have shown that the section of these nerves has 

 no such effect. Bischoff could perceive no 

 change upon the voice after he had divided 

 these nerves in two dogs.H Longet states that 

 the division of those nerves above the origin of 

 the external branch, or of the external branch 

 alone, is followed by a disagreeable hoarseness 

 of the voice.** If the variations in the length 

 of a tube alter the graveness and acuteness of 

 the sounds which it emits, we would expect that 

 the lesion of the superior laryngeals should, by 

 arresting the movements of the crico-thyroid 

 muscle, produce some change in this respect. 

 Longet believes that the crico-thyroid muscles 

 are, during their contraction, tensors of the 

 vocal chords, and that the changes upon the 

 voice induced by dividing the superior laryn- 

 geals depend upon the effect which paralysis 

 of these muscles has upon the tension of the 

 vocal chords.ft 



CEsophageul branches. Muscular contrac- 

 tions have been observed in the oesophagus on 



* Vide Haller's Elementa Physiologies, torn. iii. 

 p. 408, Lausan. 1766. 



t Observations on the Nervous System, p. 65. 



| Opus supra cit., p. 14 and 15. 



1 have seen some cases of partial aphonia in 

 the human species arising from the compression of 

 one recurrent in the upper part of the chest by an 

 aneurism of the aorta. 



|| Compendium of Physiology, p. 138, 1831. 



^ Opus cit. p. 27. 



** Dupuytren had previously maintained that 

 lesion of the superior laryngeals was followed by a 

 disagreeable hoarseness, Biblioth. Medic, toin. 

 xviii., 1807, as quoted by Longet. 



tt Opus cit, p. 8 and 27. 



irritating the trunk of the vagus, by Arnemann,* 

 Cruikshank,f Mayo,} and others. When the 

 trunk of the vagus is irritated above the origin 

 of the recurrent, the muscular fibres of the 

 oesophagus along its whole length are thrown 

 into active contraction. In experiments upon 

 rabbits we found that the oesophagus became 

 impacted with food eaten after section of the 

 vagi in the neck, when very little of it had 

 reached the stomach and when no efforts at 

 vomiting had occurred, while its muscular 

 fibres could still readily be thrown into active 

 contraction by direct excitation. From this we 

 inferred that before the presence of the ingesta 

 in this tube can excite its muscular fibres to 

 contract and propel its contents onwards, the 

 same conditions of the nervous system are ne- 

 cessary as for the production of the excito- 

 motory movements, and that certain of the fila- 

 ments of the vagi act as incident and others as 

 motor nerves. That the food also collects in 

 the oesophagus in the horse and sheep after 

 division of the vagi may be inferred from the 

 experiments of Dupuy and others. In subse- 

 quent experiments upon dogs we found that 

 substances seem to pass pretty freely along the 

 oesophagus in that animal after section of the 

 vagi, it would appear, however, that even 

 in the dog the food is occasionally retained in 

 the oesophagus ^.fter dividing the vagi.|| Arnold 

 (opus cit. p. 144) observed in his experiments 

 upon hens and pigeons that the oesophagus and 

 crop were so relaxed after section of the vagi 

 that when the animals shook their head and 

 neck, or kept the head in a depending position, 

 a quantity of chyme flowed from the bill. 



From a review of all these facts we are in- 

 clined to agree in the opinion lately expressed 

 by Dr. M. Hall, that in some animals the 

 muscular contractions of the oesophagus are 

 excito-motory, while in others they are called 

 into action by direct excitation. We cannot 

 at present determine whether the propulsion of 

 the food along the oesophagus in the human 

 species partakes more of the former or of the 

 latter class of movements. Magendie has as- 

 certained that various muscular movements gc 

 on in the lower part of the oesophagus, more 

 especially when the stomach is full, by which 

 this tube is contracted during inspiration and 

 relaxed during expiration, and that they are 

 suspended by dividing the vagi. These we 

 may class among the reflex muscular move- 

 ments. The oesophagus is endowed with little 

 sensibility, and in the natural and healthy con- 

 dition of the organ the ingesta are propelled 

 along it to the stomach without exciting any 

 sensation. From a consideration of all the 



* As quoted by Soemmering Corporis Hum. Fa- 

 brica, torn, iv., p. 272, 1794. 



t Medical Facts and Observations, vol. vii., p. 

 153, or Phil. Transact., 1795. 



$ Anatomical and Physiological Commentaries, 

 No. ii., p. 15. 



Journal de Medecine, Chirurgie, &c. Dec. 

 1846, torn. 37, p. 351. 



|| Baglivi Opera Omnia, p. 676, Anvers, 1715, et 

 Valsalvas Opera cum Epistolis Anatomicis, c. 

 J. B. Morgani Epist. Anatom. xiii. 37, Vene;. 

 1740. 



