MUSCULAR SYSTEM 103 
the biventer maxille (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 Reptiles 
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 (¢.g. Echidna, Dasypus, Pinnipedia, Lrinaceus, 
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 
