350 MORPHOLOGY OF THE TRUNK-MUSCLES. 



sheet proper, while the deeper, consisting of transverse fibres, is known as the sphincter colli. 

 From the platysma-sheet a part extends upwards behind the ear (occipito-auricular muscle) 

 and furnishes the occipitalis with the retrahens auriculam, as well as the transverse and 

 oblique muscles on the back of the pinna ; the occasional occipitalis minor (p. 296) is a 

 vestige of the primitive connection. In front of the ear the prolongation of this sheet is 

 more extensive, and undergoes greater development and differentiation : 1, a direct continua- 

 tion of the platysma-fibres over the border of the lower jaw gives rise to the depressor labii 

 inferioris and levator menti ; 2, a second portion (inferior auriculo-labial) is for the most part 

 suppressed in man, the muscles of the tragus and antitragus of the pinna being the sole 

 remains ; 3, a much larger portion (superior auriculo-labial) passes from the front of the ear, 

 where it forms the muscles of the helix, to the upper lip as the zygomatic muscles, and 

 extends upwards around the eye forming the orbicularis palpebrarum, from which again the 

 corrugator supercilii, pyramidalis nasi and levator labii superioris alseque nasi are segmented 

 off ; while above this, 4, an auriculo-frontal tract furnishes the attollens and attrahens 

 auriculam and the f rontalis. 



The deep layer, or sphincter colli, in man is suppressed in the neck, but is largely developed 

 over the lower part of the face, forming most of the musculature of the lips and mouth. 

 From it proceed the orbicularis and the muscles contributing thereto, viz., the buccinator, 

 levator anguli oris and depressor anguli oris, as well as the levator labii superioris. Continued 

 from the levator anguli oris is the compressor naris, of which the depressor alas nasi is an ex- 

 tension downwards. The depressor anguli oris makes its way to the surface through a cleft 

 in the platysma-sheet ; its inner fibres curving beneath the chin to join those of the opposite 

 side give rise to the occasional transversalis menti, and the risorius is similarly detached from 

 its outer edge. (G-. Ruge, " Untersuchungen tiber die Gesichtsmuskulatur der Primaten," 

 Leipzig, 1887.) 



