THE MUSCLES 97 



the third vertebra to the sacrum. The fibres run in an oblique 

 direction from antero-dorsal to postero-ventral. 



M. ohliquus externus profundus. Maurer (1892). 

 The deep stratum is an even thinner sheet of muscle than that just 

 described. To expose this layer it is better to commence removing 

 the superficial stratum from the ventral edge, as it is more easily 

 separable there than at the dorsal edge. It is entirely similar to the 

 superficial layer in origin and insertion, but the direction of its 

 fibres tends to become more longitudinal. 



Innervation: Both parts are innervated from the ventral rami of 

 NN. spinales 5-15. 



Function: In general both layers serve to contract the body wall 

 and consequently to compress the body cavit)^, but the specific 

 results of its action vary according to whether it is antagonistic or 

 complementary to its neighbouring muscles. 



The most internal layer of the ventral trunk muscles is, according 

 to Maurer, composed of three parts which, in higher forms, separate 

 into distinct muscles, but which, in Salamandra, are not clearly 

 separable one from another. 



The most dorsal and mesial section, lying next to the vertebral 

 column, is the pars suhvertehralis (m.s.). It passes from vertebra to 

 vertebra and is attached to the lateral part of each centrum and to the 

 ventral face of each transverse process. Its lateral edge may be 

 roughly defined as the point at which the spinal nerves emerge, but 

 apart from the separation thus caused it merges quite imperceptibly 

 into the pars transversalis. 



The pars transversalis is similarly attached to the ventral surfaces 

 of the ribs, and, at their lateral extremities, merges in turn into the 

 pars ohliqua interna. 



The pars ohliqua interna is attached to the myosepta which are 

 continuous with the ribs. 



The direction of the fibres of the several portions varies. The 

 subvertebral portion is longitudinal; the pars transversalis becomes 

 rather more oblique, while the pars obliqua interna is very 

 markedly so. The fibres of this latter portion pass from antero- 

 ventral to postero-dorsal and cross those of the M. obliquus exter- 

 nus almost at a right angle. The pars obliqua interna extends from 

 the shoulder to the pelvis. The anterior fibres are inserted around 

 the bases of the lungs and on the pericardium and help to form the 

 diaphragm (see also p. 270). The other two portions are virtually 



