MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
537 
magnus is in action, the rhomboidei will doubtless draw the scapula backwards. 
Through the combined actions of these muscles the upper part of the chest is com- 
pressed by the scapulae. 
In violent coughing and in epileptic fits, many of the muscles of the limbs act with 
great power. 
93 . Expiratory muscles acting on the ribs. 
The recti draw down the sternum, and with it the annexed costal cartilages and 
their ribs. 
The external oblique draw downwards the eight inferior ribs, bring forwards and 
downwards the posterior portions of the ribs, and compress the abdomen. 
The internal oblique draw downwards and backwards the anterior extremities of 
the inferior ribs and their cartilages, and compress the abdomen. 
The two oblique muscles, the external and internal, combine to pull downwards 
the lower ribs ; the external oblique draws the posterior curves of the ribs forwards, the 
internal oblique draws the anterior portions of the ribs and the cartilages backwards. 
94. The triangulares sterni and the transversales combine to form one large muscle , 
the constrictor of the chest and abdomen. See §§ 68 . 73 . 
We have already seen that the transversales combine with the triangulares sterni 
to form one vast constrictor of the chest and abdomen in the Porpoise, the Dog, the 
Seal and Otter. 
I find that the transversales and triangulares sterni combine in like manner in Man ; 
these muscles are indeed perfectly continuous and form one web*. 
The combined transversales and triangulares sterni may be described as one 
muscle; the constrictor of the chest and abdomen, arising from the two lower thirds 
of the sternum, the xyphoid cartilage, and the linea alba, and inserted into all the 
ribs, except the first, close to their cartilaginous attachments. The fibres of this vast 
web combine to narrow the space between all the opposite ribs ; they cause the costal 
cartilages connected with the sternum to bend on the ribs and on themselves; they 
constrict at once the space between the thoracic, intermediate and diaphragmatic sets 
of ribs, and indeed the whole chest and abdomen. 
The combined actions of the recti, the external and internal oblique, and the trans- 
versales compress the abdominal viscera, and thrust them upwards against the dia- 
phragm so as to elevate it. 
The sacro-lumbalis and the longissimus dorsi act with the quadratus lumborum to 
draw downwards the posterior portions of the ribs. 
We have then a very powerful array of expiratory muscles ; they are much more 
powerful than the inspiratory, as I previously inferred, and as has been proved by 
* Fig. XXVI. Archives of the Royal Society. 
MDCCCXLV1. 4 A 
