while in the body, had been retained in a state of over-distention, in consequence of the pressure of the internal air, not being balanced by any air between the pleuræ. Boerhaave and Haller attribute part at least of this effect to the contraction of the muscular fibres of the trachea and bronchia, but it must be observed, in opposition to such great authorities, that the contractile power of the lungs remains for a considerable time after their removal from the body, and cannot therefore depend upon a cause which must cease with the vitality of the part.

Few subjects in anatomy and physiology have caused more violent, and even acrimonious disputes, than the nature of the action of the intercostal muscles.7 Between each of the ribs are two distinct layers of muscular fibres, which are situated obliquely, but in an opposite direction, so as to decussate. It was the general opinion of the ancients, that the external layer, when it contracted, would raise the ribs, and consequently encrease the capacity of the thorax, but that the internal intercostals would depress the ribs, and of course diminish the size of the chest.

this way a measure of the elastic force of the lungs, we must ascertain the proportion which their bulk bears to that of the globe, and this to the quantity of air expelled from the lungs. Dr. Elliotson has inadvertently attributed the collapse of the lungs, when the thorax is opened, to the same cause which produces ordinary expiration; Trans. of Blumenbach, Note B. p. 82.

6 Boerhaave, Prælect. § 602. et notæ.

7 See Haller, El. Phys. viii. 1. 13; Dumas, Physiol. par. 3.

sect. 2. c. 4.

Mayow, who in so many respects outstript the science of his contemporaries, and whose works afterwards became so remarkably neglected, appears to have been the first who adopted the opinion, that both sets of intercostals, by their contraction, must raise the ribs, and thus encrease the size of the thorax.8 But his experiments and reasoning were either not attended to, or failed in producing conviction, for the old opinion appears to have been generally entertained, until the middle of the last century. The doctrine of Mayow was, however, zealously embraced by Haller," and since his time has been, for the most part, acquiesced in. But it is generally supposed that, in

8 Tract. p. 278. et seq. It is stated by Winslow, Mem. Acad. pour 1738, p. 92. and by Haller, El. Phys. 8. 1. 14. that Fabricius had previously announced the same opinion, but by referring to his treatise De Respiratione, p. 176, 7, it appears that he unequivocally supports the old doctrine.

9 Boerhaave, Prælect. t. v. par. 1. § 613 et notæ ; Haller, El. Phys. viii. 1. 12. et seq. et viii. 4. 9.; an account of his experiments on the subject is contained in his Op. Min. t. i. p. 270.. 293. Hoadley, Lect. on Respir. p. 5..8, and Hamberger were among the most zealous defenders of the old doctrine; the latter appears to have maintained it with a degree of vehemence quite disproportioned to the importance of the object, if we may rely upon the complaints of Haller, El. Phys. viii. 1. 13. Sabatier takes a directly opposite view of the subject, and supposes that both sets of intercostals will have the effect of depressing the ribs; Mem. Acad. pour 1778, p. 347; also Anat. t. iii. p. 469.

It would appear that Sommering still entertains some doubts respecting the action of these muscles: after describing the internal intercostals, and stating that their effect will be the same with that of the externals, viz. to raise the lower towards

ordinary respiration, the intercostals are not much employed, except for the purpose of fixing the ribs, and that it is only in cases of violent action of the respiratory organs, or where, from accident or disease, their ordinary action is impeded, that these muscles have any effect in encreasing the size of the thorax.2

The nature of the diaphragm, its muscular action, and its importance in the mechanism of respiration, were but imperfectly understood by the ancients. By

the upper ribs, and consequently to dilate the chest and serve for inspiration, he asks, "an costas deprimunt?" Corp. Hum. Fab. t. iii. p. 177. Murat, also, the writer of the article "Intercostals," in the Dict. Scienc. Med. conceives, that although the effect of both sets of intercostals must be the same, and that this generally is to raise the ribs, and consequently to expand the chest, yet that under certain circumstances, as where the false ribs are fixed by the action of the abdominal muscles, the contraction of the intercostals must depress the ribs, and thus contract the chest. The present Prof. Monro has committed a singular oversight in asserting that his "Father discovered, that both strata," the external and internal intercostals, "are subservient to the elevation of the ribs;" Elements v. ii. p. 9.; an oversight the more remarkable, as in a previous passage of the same work, v. i. p. 371., he had correctly attributed the discovery to Mayow.

2 The older anatomists were aware of the existence of cases, where the cartilages of the ribs were ossified, so as to prevent the action of the intercostals, without any material impediment to respiration. Winslow ubi supra; Fabricius de Respir. c. 10. sub finem. For farther information on this subject the reader may consult Borelli, par. 2. prop. 81..95. Bellini, lem. 11.; Senac, Mem. Acad. pour 1724: Winslow, idem pour 1738; also Anat. Sect. 9.6; Boerhaave, Inst. § 615; ditto Prælect. passim; Haller, El. Phys. lib. viii. passim ; Dumas, Physiol. par. 3. § 2. c. 4; Richerand, Physiol. p. 199. et seq.

some it was supposed to possess a kind of independent life, by others it was thought to be the seat of the soul, and it was generally regarded as possessed of some very mysterious or inexplicable power, until Fabricius, at the beginning of the seventeenth century, explained its action and properties upon correct principles. It is now universally regarded as the great agent by which the size of the cavity of the thorax is regulated; in its natural or relaxed state, it is arched up, so as to diminish the capacity of the chest, while this is necessarily encreased, when it is flattened by the contraction of its muscular part.*

Malpighi, to whose researches we are indebted for our knowledge of so many parts of minute anatomy, appears to have been the first who described the structure of the apparatus by which the air is distributed through the lungs and is enabled to act upon the blood, and the description which he gave of the parts has been generally supposed to be correct. Succeeding writers, as is too frequently the case, while they have professed to adopt the ideas of their predecessors, have indulged their imagination in inventing a disposition of the parts, which cannot be found in

3 De Respiratione, lib. ii. c. 8.

4 For an accurate description of the diaphragm and its action and uses, as well as for a very copious list of all that had been published concerning it before his time, Haller's treatise in his Op. Min. t. i. p. 249, may be consulted, as also his experiments on the motion of the diaphragm in living animals. Ibid. p. 293.. 300. et Mem. sur les Part. irrit. et sens. t. i. p. 65. et seq. See Albinus's Tab. musc. No. 14. fig. 4. 5. 6. 7.

s Epist. de Pulmonibus, i.

the original account of them, and which has probably no actual existence. Willis, for example, gives a figure of a portion of the lungs, according to which they consist of a congeries of rounded vesicles, separated from each other, and every one of them provided with a distinct tube, so as to resemble a bunch of grapes, a structure which has probably no existence. On the other hand, Helvetius endeavoured to prove that the bronchia terminate in a cellular or spongy tissue, composed of a membranous substance, the cells of which have no determinate figure or regular connexion with each other. But, upon the whole,

6

8

6 Pharm. Rat. p. 2. tab. 3. fig. 1. Cheselden, Anatomy, p. 173, remarks upon Willis's description, that it is "imaginary and false, as he could not but have known, if he had ever made the least inquiry into the lungs of any animal."

7 Malpighi's description of the parts is as follows: "Diligenti indagine inveni totam pulmonum molem, quæ vasis excurrentibus appenditur, esse aggregatum quid ex levissimis et tenuissimis membranis, quæ extensa et sinuatæ pene infinitas vesiculas orbiculares, et sinuosas efformant, veluti in apum favis alveolis ab extensa cera in parietes conspicimur." " Membranæ ista vesiculæ videntur efformari ex desinentia tracheæ, quæ extremitate, et lateribus in ampullosos sinus facessens, ab his in spatia, et vesiculas inequales terminantur.” See plate to the Epist. de

Pulm.

8 Mem. Acad. pour 1718. p. 18. Helvetius appears, however, to have been influenced in his opinion by the texture of the lungs in the amphibia, which, as they differ from the human in the relative sizes of the component parts, may do so likewise in the connexions of these with each other. An account of the characteristic difference between the lungs of the warm and the cold-blooded animals may be found in Shaw's Lectures, v. ii. p. 2, 3.