278 COMPARATIVE ZOOLOGY OF CHORDATES 



intercostal muscles in the thorax, and the muscles of the 

 abdominal wall. 



The simple segmental arrangement of the myotomes which 

 is so characteristic of Amphioxus and lower Craniates, tends 

 to be obscured and lost in the Tetrapods. 



With regard to the dermal musculature, the muscles 

 attached to the hair-follicles (arrectores pili) are smooth and 

 innervated by sympathetic fibres. The panni cuius carnosus 

 muscles are derived from the striped muscles of the trunk and 

 are therefore innervated by ventral nerves. The platysma 

 muscles, and the muscles of expression are derived from the 

 striped muscles of the 2nd visceral arch, and consequently 

 are innervated by the facial nerve. 



Literature 



Maurer, F. Die Entwicklung des Muskelsystems und der elektrischen 

 Organe. Hertwig's Handbuch der verg. und exp. Entwicklungslehre 

 der Wirbeltiere. Part 3. Fischer, Jena, 1906. 



VAN Wijhe, J. W. Ueber die Mesodermsegmente und die Entwicklung der 

 Nerven des Selachierkopfes. de Waal, Groningen, 1915. 



