BY W. J. McKAY. 961 



In the non-venomous snakes, with the disappearance of the 

 hypapophyses, the trans versalis is continued inwards as a sheet of 

 fascia, containing a slight amount of muscular tissue, and is 

 inserted on the anterior common ligament, coalescing with the 

 fascia that gives origin to the depressores costarum in this region. 

 We see therefore that the transversalis very distinctly arises from 

 the vertebral column in non-venomous snakes, and that in venom- 

 ous snakes the very slight layer of fascia found beneath the 

 depressors is the representative of this sheet, which corresponds 

 to the anterior lamella of the tendon of origin of the transversalis 

 in higher animals. 



With regard to the two sheets of muscle bundles making up 

 the main body of the muscle, the external one has its fibres 

 arranged in bundles, the direction of the fibres being from without 

 inwards and forwards, corresponding to the direction of the 

 retrahentes costarum, and therefore having such a direction as a 

 subcostal group of muscles would take. The layer corresponds 

 with D'Alton's dussere Bauclmitoskel. The inner layer has its 

 bundles of fibres placed in a direction corresponding to a true 

 transversalis muscle. 



M. DEPRESSORES COSTARFM. 



M, costo-verteh^ales su2Jeriores, Hofi"mann; Inner er, grosser Rilck- 

 wdrtszieher der Eipjjen, D'Alton ; Costales inierni superiores, 

 Hiibner ; Transver so-costal, R. Jones ; Retrahentes costarum, 

 Owen. 



The depressores costarum arise from the extremities and sides 

 of the hypapophysis. The muscular bellies coalesce at their origin, 

 and then run forwards and outwards, each to be inserted by a 

 tendon on the middle of the posterior border of the fourth rib 

 from the origin, at the same time giving slips to the ribs over 

 which they pass. This is the arrangement in venomous snakes, 

 but in Morelia a considerable change takes place with the dis- 

 appearance of the hypapophysis. Instead of the muscular bundles 

 arising directly from the vertebrae, they now arise by means of a 

 strong aponeurosis attached to a well marked anterior common 



