MUSCULAE SYSTEM OF VERTEBRATA. 493 



distinguislied by its deeper colour^ may be regarded as belonging to 

 tbis system. In tbe Ampbibia tbere are dermal muscles in tbe 

 bead, wbicb act on tbe nasal orifices, and, in tbe Anura, in tbe 

 anal region also. Tbe muscles lying on tbe external nares are better 

 developed in tbe Eeptilia. Tbe dermal muscles are of great func- 

 tional importance in tbe Opbidii, as tbey produce a movement of tbe 

 scales, wbicb is of use in locomotion. 



In Birds tbere are laro*e flattened dermal muscles in various 

 parts of tbe body ; as in tbe Reptilia (Cbelonii) tbere is a continuous 

 layer of muscles in tbe neck; otber dermal muscles take tbeir origin 

 from tbe skeleton, sucb, for example, as tbe muscub patagii, wbicb 

 pass into, and extend tbe membrane of tbe wing*. Tbe muscles 

 wbicb serve to move tbe remiges and rectrices also belong to tbis 

 category. 



Tbe dermal musculature is more bigbly developed in tbe Mam- 

 malia. Tbere is generally a large muscle below tbe integument of 

 tbe trunk, wbicb covers tbe dorsal region of tbe body, and is con- 

 tinued on to tbe bead and neck ; tbis is inserted by tendinous 

 pieces into different portions of tbe integument, wbile anteriorly it 

 is also inserted into tbe bumerus. It is best developed in Ecbidna, 

 Dasypus, and in Erinaceus, wbere it forms tbe muscle by wbicb tbe 

 body rolls itself up. In most of tbe Apes tbe large dermal muscle 

 is distributed over tbe same parts as in otber Mammals, but it is 

 more distinct in its anterior portion. In tbe Orang and Cbimpanzee 

 tbis latter is represented by a muscular plate, wbicb occupies tbe 

 sides of tbe neck, and is continued on to tbe face ; in Man it is 

 reduced to tbe platysma myoides. 



Musculature of the Skeleton. 

 § 372. 



Tbe differentiation of tbe muscles, wbicb is due to tbe connec- 

 tion between tbe muscular system and tbe skeleton, is very inti- 

 mately connected witb tbat of tbe skeleton, inasmucb as botb parts 

 have always reciprocal relations, owing to tbeir being botb formed 

 for tbe same function. Wben, tberefore, any portion of tbe skeleton 

 is increased in size, tbe muscles tbat go to it are also increased, and, 

 wben anotber part undergoes atropby, its muscles are correspond- 

 ingly diminisbed. So, also, tbe greater functional independence of 

 tbe muscles is bound up witb a greater differentiation. 



Tbis differentiation gives rise to a number of systems of muscles, 

 eacb of wbicb can be again divided into subordinate complexes of 

 more or less distinct muscles. Tbe muscles of tbe trunk, of tbe 

 cepbalic skeleton, and of tbe appendages, may be distin- 

 guisbed as systems of tbis kmd. 



Tbe above-mentioned primitive musculature gives rise to tbe 



