MUSCULAR SYSTEM 103 



the biventer maxillae (digastricus) and the mylohyoid (as may be 

 gathered from their innervation), while the posterior belly of the 

 former may sometimes fuse with the stylohyoid. 



Undoubtedly the most interesting of all the retrogressive 



muscles of the cervical region is the so-called platysma myoides 



(subcutaneus colli). This muscle is also related, as will be 



shown later, to certain cephalic muscles, and requires a more 



detailed description (cf. infra, pp. 104 and 114). 



Whereas most muscles are closely connected with the skeleton, 

 there are, in the Vertebrates, certain muscles which both arise 

 from and are inserted into the integument or the subcutaneous 

 tissues. These are the cutaneous muscles (panniculus carnosus 

 of the lower Mammalia). 



These cutaneous muscles are [with rare exceptions] only 

 feebly developed among Fishes and Amphibia, but in Eeptiles 

 and Birds they play a great part in connection with the scutes, 

 scales, and feathers. They are, however, most developed in 

 Mammals, in which they may spread like a mantle over the back, 

 head, neck, and flanks (e.g. Echidna,Dasypus, Pinnipedia, Erinaceus, 

 and others). 



In Man and the Anthropoids only feeble traces of this 

 musculature are found, such as the platysma-myoides already 

 mentioned, which spreads over the upper part of the thorax and 

 the neck and partly over the face (cf. Fig. 67). Other slight 

 traces are found in the shoulders, back, abdomen, axilla, forearm, 

 hand, and buttocks. 



Among the lower Mammalia the panniculus carnosus functions 

 as a protective against injury to the skin. The reaction of the 

 skin of horses when stung by insects may be given as an example 

 of this. 



The mimetic musculature is very closely connected with the 

 cutaneous, and is at least partly to be derived from it phylo- 

 genetically. In a general sense, the differentiation of the 

 mimetic musculature may be said to advance with advancing 

 intelligence ; and we may therefore expect to find it most highly 

 developed in the Primates. 



The phylogenetic development of this system has been 

 studied by Gegenbaur and Ruge. According to Gegenbaur, the 

 human platysma appears to be the remnant of a musculature 

 which was continued on to the head, but which has only retained 

 its primitive undifferentiated condition on the neck. The chief 

 reason of this is that the platysma, even in Man, is sometimes 



