Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
2«2 DESIGN IN NATURE<br />
trunk (thoracic and abdominal portions) as forming a large oval-shaped cylinder closed at both ends and divided into<br />
two by a movable muscular partition—the so-called diaphragm to which allusion has already been made (Fig. 47, A, B).<br />
The muscles forming the cylinder are arranged in straight, curved, sUghtly obhque, oblique, very oblique, and<br />
transverse lines ; bones being inserted among them to afford attachment and leverage. The respiratory movements<br />
begin and terminate in the muscles, aided by the elasticity of the ribs and other structures.<br />
The straight muscles occur chiefly on the anterior and posterior aspects of the trunk ;<br />
and transverse ones are found on all the aspects.<br />
the oblique, very oblique,<br />
Similar muscular arrangements are met with in the ventricles of the mammalian heart, in the face and neck,<br />
in the pharynx and larynx, and in the anterior and posterior extremities. They are repetitions of the primary or<br />
typical muscular arrangements which obtain in the hollow viscera.<br />
The straight muscles on the anterior aspect of the body are the rectus sternahs or sternahs brutorum (an occa-<br />
sional muscle) (Quain, p. 243), the rectus abdominis, and the pyramidalis. The last two muscles draw down the<br />
sternum, ribs, &c., in expiration.<br />
The straight muscles on the posterior aspect of the body are the quadratus lumborum and the dorsal muscles,<br />
some of which are inserted into the ribs posteriorly. They fix the spinal column and posterior portions of the ribs<br />
in forced respiratory movements.<br />
The obhque and very obhque muscles on the anterior aspect of the thorax are the pectoralis major and minor,<br />
to which may be added the deltoid. These afford fixed points in difficult breathing.<br />
The oblique and very obhque muscles on the posterior aspect of the body are the trapezius, latissimus dorsi, supra<br />
spinatus, infra spinatus, and rhomboidei, These also afford fixed points in difficult breathing.<br />
The oblique muscles on the lateral aspects of the thorax are the external and internal intercostals. These elevate<br />
the ribs in inspiration.<br />
The oblique muscles on the lateral aspect of the abdomen are the external and internal oblique muscles. They<br />
draw down the ribs in expiration.<br />
The transverse muscles in the thorax and abdomen are the serratus magnus, the serratus anticus and posticus,<br />
and the transversalis abdominis. They contract and expand the thorax and abdomen as required.<br />
A combination of all these muscles, as far as the direction and arrangement of their muscular fibres are con-<br />
cerned, is found in the diaphragm. In it, as explained, the muscular fibres run in straight lines, obliquely, very<br />
obliquely, and transversely.<br />
Authorities are not agreed as to the number of muscles which take part in the respiratory movements either in<br />
calm, normal respiration or in forced, violent respiration.<br />
As a matter of fact, nearly all the muscles of the body may take part in the respiratory movements if they be<br />
very violent, as in asthma, severe dyspnoea, &c. In these cases the muscles of the neck, chest, abdomen, and even<br />
the superior and inferior extremities are brought into play. The neck muscles connect the head with the upper<br />
part of the thorax and afford fixed points : the muscles attached to the upper part of the humerus (when this is<br />
elevated), as the shoulder, scapulae, and chest muscles, afford additional fixed points, and even the muscles of the lower<br />
extremities attached to the pelvis perform a similar role.<br />
The number of muscles which take part in the respiratory movements is determined by the violence of the<br />
respiratory acts, but even in calm or normal breathing the number is considerably in excess of those usually stated,<br />
and I have to express my conviction that in every respiratory effort not only the muscles of the thorax, but also those<br />
of the abdomen are engaged ; the thoracic and abdominal muscles, as indicated, being co-ordinated and acting<br />
together ; the thoracic muscles shortening when the abdominal muscles elongate, and vice versd. The thoracic and<br />
abdominal muscles act quite apart from elasticity as a moving force.<br />
This is a new explanation of the respiratory movements, but one to which I attach much importance,<br />
as it brings the thoracic and abdominal nmscles into Une with the muscles of the mammahan heart, which<br />
are typical.<br />
It will simphfy matters to regard all the muscles with fijced points above the ribs as muscles of inspiration,<br />
and those with fixed points below the ribs as muscles of expiration. It may be stated in this connection that there<br />
are two large muscles (the recti abdominis) to which hitherto no adequate function has been assigned. The recti<br />
abdominis are doubtless muscles of expiration, and when they close or contract they pull the sternum, and the ribs<br />
connected with it, downwards and inwards. This they do by a powerful direct pull. The external and internal<br />
intercostal muscles are wholly concerned in elevating the ribs, which they do in conjunction with other muscles. By<br />
their contraction they are largely instrumental in raising the ribs, and act as muscles of inspiration. The inter-<br />
costal muscles do not act separately and in opposite directions, as is usually stated. They act simultaneously and<br />
in the same direction. Their positions and connections, and the mode in which the ribs are jointed to the vertebral