Why does phthisis attack the apex of the lung? : a discussion at the Medical Society, London Hospital, October 29th, 1903, opened by Dr. Arthur Keith.

  • Keith, Arthur, Sir, 1866-1955.
Date:
[1903?]
Catalogue details

Licence: In copyright

Credit: Why does phthisis attack the apex of the lung? : a discussion at the Medical Society, London Hospital, October 29th, 1903, opened by Dr. Arthur Keith. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    A thorax in the position of extreme inspiration, viewed from above. The part of the thorax thus seen makes up what is described in tlie text as the anterior wall of the thorax. The cross^ mark the position of the great fissure of the lung. Part of the spinal wall is also seen. at once, is absent in the first, second and third costal arcs; it begins in the fourth, and increases, both in length and obliquity, from the fourth to the eighth ; after the eighth the lateral segment diminishes in length and has disappeared in the twelfth. These lateral segments are nearly on the same plane and are not seen when the thorax is viewed from above (Fig. I.) They form the peculiar flattened area which everyone must have noticed on the side of the dried and mounted thorax. In people with wide chests {i.e., flattened from back to front) the lateral segments are com- paratively short; in round and narrow chested people [i.e., flattened from side to side) these segments are long. The characteristic of the ventral segment of the costal arcs is {see Fig. I.) that each succeeding segment from above down- wards is part of a greater circle than the one above it. When the thorax is viewed in profile from above, each of the ventral segments is seen standing out further forwards than the one above, whereas we have seen that in the lateral segments the last segment is on the same plane as the first. The cartilages are included in the ventral segments; each succeeding cartilage from the first to the eighth is longer than the one above it, and more obliquely placed. Beyond the eighth rib the ventral segments cease to exist. Relative functions of the lateral and ventral segmetits of the costal arcs. Since each of the ventral segments of the ribs stands out some distance in front of the one above it, it is plain that, when these segments are elevated, all that part of the lung which lies beneath them is directly expanded forwards. Now if you look at the part of the lung which lies beneath the ventral segments, you will see that it is exactly the costal surface of the upper and middle lobes of the right lung, and the upper lobe of the left lung (Fig. I.); that is to say the line of demarcation between the ventral and lateral segments of the costal arcs corresponds to the great fissure of the lung. It will be seen that this observation is an approach towards the solution of a problem which has never been explained—“Why is the lung divided into lobes } ” Since each costal cartilage increases in length and obliquity from above downwards, it is plain that the elevation of the cartilages will also cause an increase in the transverse diameter of the chest. Thus the ventral seg- ments of the costal arcs cause, by their elevation, a direct enlargement forwards of the area of the lung beneath them, and indirectly an enlargement of the transverse diameter of the chest, which is attended by an expansion of the lung on their lateral surface. The lateral segments of the costal arcs cover the lateral surface of the lower lobe of the lung, and have a direct action in expanding that surface, and an indirect effect in the expansion of the ventral surface in the following manner i—when the lateral segments are ele- vated by the external intercostals, they not only move upwards, but also outwards. The outward movements cause a direct expansion of the lateral surface of the lung; the upward move- ment, since each lateral segment increases from the fourth to the eighth, leads to an increase in the antero-posterior diameter of the thorax, and therefore to an expansion forwards of the ventral surface of the lung. The lateral seg- ments, however, decrease from the ninth to the twelfth ribs, therefore the elevation of the lower segments, while they do cause an increase in the lateral diameter of the chest and a direct expansion of the underlying lateral surface of the lung, lead to a decrease of the antero- posterior diameters. The muscles of respiration. As a rule the first to be enumerated amongst the muscles of respiration are the levatores costarum, which are not in any sense respiratory, but spinal muscles. The muscles of the abdominal wall on the other hand are usually included in the list of extra- ordinary muscles of respiration, and yet no one