. Annales du Musée de l'Afrique du Sud  = Annale van die Suid-Afrikaanse Museum. L'histoire naturelle. RC.POST MIN OBLC CR R C ANI. RC.POST, le MAJ. C OBL GAUD '3' (b) Fig. 50. LystrosauTus murrayi. Nat. Mus. N° C.6457. Complexe atlas-axis avec musculature restauré en (a) les déplacements latéraux et {b) vue dorsale. les muscles et Evans (1939) appelle l'obliquus capitis supérieur et inférieur, agir respectivement pour la rotation de l'atlas sur l'axe, et l'extension de la tête à l'atlantal occipito-joint. La restauration de l'obliquus capitis et rectus muscles dans un therapsid comme Lystrosaurus est compliqué b

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. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. RC.POST MIN OBLC CR R C ANI. RC.POST, MAJ. OBL C GAUD '3' (b) Fig. 50. LystrosauTus murrayi. Nat. Mus. No. C.6457. Atlas-axis complex with restored musculature in (a) lateral and {b) dorsal views. muscles, which Evans (1939) calls the obliquus capitis superior and inferior, serve respectively for rotation of the atlas about the axis, and extension of the head at the occipito-atlantal joint. The restoration of the rectus and obliquus capitis muscles in a therapsid such as Lystrosaurus is complicated by uncertainty as to the number of 'mamma- lian' features evolved in the genus, such as, for example, the amount of rotation possible at the atlanto-axial joint. Since the Dicynodontia became a distinct group early in the evolution of the therapsids, and are phylogenetically very distant from the ancestral mammal stock, any so-called mammalian charac- teristics most probably evolved independently, and should be regarded as parallels to similar qualities in, for example, the cynodonts. Of importance in this connection is the basically reptilian interpretation by Jenkins (1968) of the cynodont atlas-axis complex and the associated musculature. Cox (1959) has also chosen an essentially reptilian reconstruction of the atlas-axis musculature in the dicynodont Kingoria, supposing that the primitive obliquus capitis magnus muscle was present between the axis and occiput. However, Ewer (1961) states that the obliquus capitis magnus muscle was probably not present in any of the therapsids, and that Daptocephalus was capable of fairly extensive rotatory movements at the atlanto-axial joint. In Lystrosaurus, judging by the rudimentary condition of the pre- and postzygapophyses of the axis and atlas respectively, some degree of rotation did take place at this joint, and since the obliquus capitis magnus muscle would have impeded this motion, it was probably not present, at least not as an i

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