BY W. J. McKAY. . 951 



In Morelia the levatores form the prominent muscular column 



on the inferior surface of the vertebral column when the depressores 



have been reflected, while the subvertebral rectus is but slightly 



developed. In Acanthophis and in all venomous forms that we have 



examined, the subvertebral rectus forms the prominent column, the 



levatores being insignificant. This peculiarity has not been before 



pointed out. 



Mm. intercostales externi. 



Mm. intercostales proprii, Hofimann ; Zwischenrippenmusheln^ 

 D' Alton and Meckel ; Intercostal, K. Jones, Owen. 



The external intercostals spring from the posterior and inferior 

 surface of one rib, and are inserted on the anterior surface of the 

 rib immediately behind. The muscle extends from the head of the 

 rib to the extremity, where the costal cartilages arise. The 

 muscular fibres run from before backwards and outwards, taking 

 the usual direction of external intercostal fibres. Between the 

 intercostal cartilages the fibres run more antero-posteriorly, and so 

 this portion of the muscle is usually described as though it were a 

 distinct muscle. 



On comparing this portion of the muscle to the corresponding 

 portion in Hydrosaurus, we find that the same alterating in the 

 direction of the fibres has occurred but to a less degree, and the 

 muscle is so obviously but a continuation of the external inter- 

 costals, that we do not see the necessity for a distinct name. 



Hofi'mann has named these antero-posterior fibres Mm. retra- 

 hentes costarum breves; D' Alton, Muskeln zwischen Rippenhnorpeln; 

 Hlibner, Intercostales recto-decursu hinas costas intercedentes ; 

 Meckel, Gerader Bauchmuskel ; Owen, Rectus abdominis. 



The intercostals are covered superiorly by the levatores costarum, 

 and the pretrahentes superiores and inferiores. Inferiorly they 

 are separated from the depressores costarum by the intercostal 

 nerves. The main portion of the latter pierces the muscle, so as 

 to gain the superior surface, at a point where the depressores are 

 inserted into the ribs, and on arriving at the surface supplies the 

 pretrahentes group. 

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