MUSCULAR 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 
Mm. orbito-auric. Mm. helicis 
im. aurie. sup / 
1 
> i} 
Witrne) 
m. awriculo 
antitrag. 
labial. 
A ~~ m. mandi- 
bulo-awricul 
Fig. 68.—SUPERFICIAL MUSCULATURE OF THE FAcE IN Lepilemur mustelinus. 
(After Ruge.) The deeper layer (m. sphincter collt) 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 
nuche. Schultze found this in eighteen out of twenty-five 
bodies, Macalister in 35 per cent; others, however, have been 
less fortunate. It was always found to be symmetrical, 7. 
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 auricule. 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. 
