(From inter, between, and cos-tee, the ribs,) any part situated between the ribs; viz.

Intercqstales arteriae, which arise in pairs from the aorta, and run on' the lower parts of each rib. They are eight, nine, or ten in number, of which the upper come from the subclavian. The intercostales of the true ribs anastomose with the internal mammary; those of the superior go to the muscles of the telly.

Intercostales musculi; mesopleurioi; intercostal musci.es are eleven in number on each side externally, and as many internally; in all forty-four. The external ones pass downwards and forwards; rising from the edge of the superior, and inserted into that of the inferior, rib: their fibres run nearly parallel; but near the sternum disappear. Their use is to elevate the ribs. The internal ones are the reverse of the external; rising from the edges of the inferior, and inserted into those of the superior, ribs; consequently they decussate each other. These depress the ribs; so that, by the alternate action of the two sets of muscles, the thorax is expanded in inspiration, and diminished in capacity during expiration.

The levatores costarum longiores and breviores of Albinus are those portions of the external intercostals which arise from the the transverse processes of the vertebrae, where the ribs are fixed to them, and other portions which pass over one rib and terminate in the next below it. Similar portions of the internal are called by Douglass costarum defiressores proprii Cowperi.

Intercostales nervi; intercostal nerves, sym-pathetici nervi majores, are formed of all the spinal nerves, and of branches from the fifth and sixth pairs from the brain. They run on the other side of the ribs. This is a very important part of the nervous system; but it has already claimed a large share of our attention. See Cerebrum.

Intercostales venae, dextrae, superiores, et inferiores. See Azygos.