On the internal or parietal surface of the left ventricle in man and in mammals are two papillary muscles, which are almost identical and well developed. In man, these muscles are known as the m. papillaris parietalis anterior sinister and the m. papillaris parietalis posterior dexter, in mammals, the m. papillaris parietalis cranialis sinister and caudalis dexter, or, in shorter form, mm. papillaris parietalis sinister et dexter. In the right ventricle in man, there are two papillary parietal muscles: the mm. papillares anteriores et posteriores. On the septum of this ventricle there is, as in mammals, a muscle called the m. papillaris septalis medialis seu subarteriosus. Beside it are one or several smaller muscles, varying from one individual to another: the mm. papillares septales accessorii seu parvi. In the right ventricle of the mammalian heart is found, in addition to the m. parietalis septalis subarteriosus, already mentioned, a m. papillaris caudalis, more or less well developed in some species and, in the majority of mammals, the m. papillaris septalis cranialis, which is always well developed. In certain mammals, there is, in rare cases, a m. papillaris septomarginalis seu parietalis. It may be said, in conclusion, that, in a large number of mammals, there is, on the internal surface of the external wall of the right ventricle, a reasonably well developed m. papillaris parietalis.
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