MUSCULAE SYSTEM 



105 



origin. In time the eyes, forehead, temples, and the parietal 

 region were reached. 



In the Lemuroidea the mimetic muscles, instead of being 

 sharply individualised as in Man, are not anatomically distinct, 

 i.e. they are merely parts of a great muscular tract, in which a 

 superficial and a deeper layer can be distinguished (cf. Figs. 68 



m. orbito-auric. 



m. levator labii 



m. orb. oculi 



m. helicis 



i. auriculo \ sup 

 labial. J it\ 



FIG. 68. SUPERFICIAL MCJSCULATURE OF THE FACE IN Lepilemur mustelinus. 

 (After Euge.) The deeper layer (m. sphincter colli) is visible in the neck. 



and 69). The superficial layer is the platysma, the deeper the 

 so-called sphincter colli. 



In those exceptional cases in Man, in which the cervical 

 portion of the platysma is developed, it is called the transversus 

 nuchse. Schultze found this in eighteen out of twenty-five 

 1 todies, Macalister in 35 per cent; others, however, have been 

 less fortunate. It was always found to be symmetrical, i.e. 

 developed on both sides. This muscle, which is almost always 

 present in the human embryo, corresponds in position with the 

 protuberantia occipitalis ; from this it radiates outwards along 

 the linea semicircularis, towards the tendon of the sterno-cleido- 



muscles split off from it. It is also found in Reptiles (Saurians and Chelonia). In 

 Crocodiles a vestige of it is found in the powerful levator auriculae. Even in 

 Amphibians and Sharks this muscular tract is already developed, and from it can be 

 derived those human muscles which are innervated by the ramus auricularis posterior 

 nervi facialis. 



