BY W. J. McKAY. 941 



spinalis of Hydrosaurus. The muscle is supplied by the internal 

 branches of the posterior primary divisions of the spinal nerves. 



M. SEMISPINALIS DORSI. 



The tendons of the semispinalis arise from the flattened surface 

 on the upper side of the postzygapophysis. Running upwards, 

 forwards and inwards, the tendons end in well marked bundles of 

 muscle, which fuse with the under and lateral portions of the 

 spinalis, and so are indirectly inserted into the neural spines. The 

 tendons of origin are closely connected with the aponeurosis 

 covering in the multifidus beneath. 



In Morelia in addition to the muscular bundles that are devel- 

 oped at the extremities of the tendons, there are a number of 

 leaves of muscle which spring from the anterior border of the 

 tendons, and also from the vertical aponeurosis of the longissimus. 

 These bandies give rise to what appears to be a distinct series of 

 muscles running between the semispinalis and the longissimus. 

 This series is called by D' Alton, Zweiter oder kurzer absteigender 

 Muskel zivischen den Gelenhen und Dornfortsdtzen ; by Hubner, 

 M. spinoso-vertehralis ; by Meckel, Vieltheiliger Eilckgratsmuskel ; 

 by Hoffmann, postzygajyophyses-sjnnales. In Hydrosaurus there 

 is an intermediate arrangement between what we see in Acanthophis 

 and Morelia, the second series becoming united with the first. We 

 therefore consider that the bundles in Morelia are but specialised 

 portions of the semispinalis proper. The internal divisions of the 

 nerves run up and pierce the multifidus, and then lie between it 

 and the semispinalis, supplying the latter and the spinalis, at the 

 same time giving branches to the accessory bundles in Morelia. 



M. MULTIFIDUS SPIN^. 



Mm. neuro-spinales, Hoffmann ; Muskel zwischen der Wir- 

 helhogen und den Dornfortsdtzen^ D'Alton. 



The multifidus arises from the lower part of the lateral surface 

 of the neural spines, immediately beneath the origins of the 

 spinalis. It also arises from the general fascia that stretches 

 between the neural spines and zygapophyses, separating it from 



