364 ELEMENTARY ANATOMY. [LESS. 



Considered independently of the bony skeleton, the muscu- 

 lar system may, as its simplest expression, be conceived as a 

 fleshy, antero-posteriorly extended envelope of the body, cut 

 up, at regular intervals, into a series of successive segments, 

 by means of transverse aponeurotic membranes extending 

 outwards from the body axis to the skin. 



From this primitive condition the muscles of the back may 

 be conceived as arising by means of increasing obliquity, 



4 3 



FIG. 322. DIAGRAM o? CAUDAL MUSCLES OF RIGHT SIDE OF TAIL OF Iguana, 

 showing the obliquity of the aponeurotic intersections of the muscular 

 portions which are themselves drawn out into cones yet preserving a 

 numerical relation to the supporting vertebrae. 



JV, neural spine : //, hypapophysial spine ; z, zygapophysis ; t, transverse pro- 

 cess ; i, dorsal series of cones ; 2, upper lateral series of cones ; 3, lower series 

 of cones ; 4, ventral series of cones. 



conical prolongation, and partial detachment (from muscle) 

 of the aponeuroses, together with condensation of their pro- 

 duced ends till the latter become firm tendons, directed more 

 or less obliquely forwards the muscular fibres, in the mean- 

 while, taking slightly different directions at different depths. 



The muscles of the abdomen may be conceived as arising 

 through atrophy of the transverse aponeuroses (of which the 

 linece transverse of the rectus are the last remains) and 

 differentiation of the muscular mass into superimposed 

 sheets of differently directed fibres. 



The muscles of the limbs may be conceived * as arising as 

 conical sheaths of muscular fibres investing protruding limb- 

 rudiments, and becoming divided and annexed to successive 

 limb-segments as such limb-rudiments become developed 

 and segmented finally assuming the form of a median and 

 two lateral groups of muscles both on the extensor and flexor 

 surfaces of each limb. 



1 As has been suggested by Professor Humphrey, F.R.S. 



