MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
541) 
PLATE XXIX. 
Illustrates the position of the ribs and the action of the external and internal inter- 
costal muscles in expiration and inspiration in Man. 
Fig. XIII. a.b. Are front views. 
Fig. XIV. a.b. Side views ; and 
Fig. XV. a.b. Dorsal views in the young and the adult man. 
In figs. XIII. a., XIV. a ., XV. a., the lungs are flaccid (expiration). 
In figs. XIII. b., XIV. b., XV. b., the lungs are distended (inspiration). 
These views were taken by aid of a tracing frame (§ 4), and reduced by a penta- 
graph. 
These figures demonstrate that during inspiration (§§ 1.4) 
The five superior ribs, the thoracic set, approach each other. 
The four inferior ribs, the diaphragmatic set, recede considerably from each 
other . 
The sixth, seventh, and eighth ribs, the intermediate set, recede slightly from 
each other (^ 81). 
The dorsal arch is deepened and shortened (§§ 80.81). 
The external intercostals of the thoracic set of ribs are throughout inspiratory. 
The external intercostals of the diaphragmatic set are, in front, expiratory ; behind, 
inspiratory. 
The external intercostals of the intermediate set are throughout inspiratory, being 
feebly so to the side (§ 85). 
The eighth external intercostal is behind inspiratory; to the side, expiratory ; and 
in front, acting from the fixed on the floating cartilage, inspiratory. 
The internal intercostals are all expiratory behind. 
The internal intercostals are inspiratory between the costal cartilages of the tho- 
racic set of ribs. 
The internal intercostals are inspiratory between the ribs of the thoracic set in 
front, where they approach each other during inspiration. 
The internal intercostals between the diaphragmatic and intermediate sets of ribs, 
are throughout expiratory (§ 85). 
The following additional drawings, illustrative of the paper, are deposited in the 
Archives of the Royal Society. 
Fig. XIX. a.b. The female (§ 9/), 
Fig. XXI. a.b. and fig. XXII. a.b. The child 99), 
Fig. XXIII. a.b.c.d. The old man (§ 100), 
Fig. XXIV. The foetus, and 
