132 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
With the development of the paired appendages into organs for the 
support of the body (tetrapoda) the skeleton of the leg is converted into 
a series of levers, and the intrinsic muscles are correspondingly dif- 
ferentiated and developed. Details cannot be given here as there are 
so many modifications, but they may be grouped as flexors, which 
bend the limb or its parts; extensors which straighten it, and rotators 
which turn it on its axis. These undergo the most modification in the 
peripheral regions, the muscles of the upper arm and thigh being more 
constant in character and position. Even more constant are the ex- 
trinsic muscles, which may be grouped as in fishes. Most prominent 
Mi 
LEE | 
LEZ iy iy 
Wy, i 
UYU YE? 
Fic. 140.—Superficial muscles of anterior part of Salamandra maculata, after Fiir- 
bringer. a, anconeus; bi, humero-branchialis inferior (biceps); bs, levator scapul; cuc, 
cucularis; dir, dorso-trachealis; dg, digastric; ds, dorsalis scapule; eo, external oblique; 
id, latissimus dorsi; m, petro-tympano-maxillaris (masseter); mh, mylohyoid; pc, pectoralis; 
ph, procoraco-humeralis; ra, rectus abdominis; spc, supracoracoid. 
of the levators of the fore limb are the trapezius and levator scapule 
muscles, while the pectoralis and serratus anterior act as depressors; 
the sternocleidomastoid and the levator scapule anterior act as 
protractors, the pectoralis minor and the latissimus dorsi are their 
antagonists. In the pelvic region the extrinsic muscles are less dif- 
ferentiated in function. The pectineus and adductors act as pro- 
tractors, the pyriformis counteracts them; the limb is drawn toward 
the middle line by a pubofemoralis, while the gluteus muscle acts as 
a retractor and elevator. ; 
THE VISCERAL MUSCLES. 
In the gill-bearing vertebrates a special system of muscles is devel- 
oped in connection with the visceral arches, which have to open and 
close the visceral clefts, including the mouth. With the loss of the gills 
some of these muscles are lost while others become changed in function, 
several retaining their connection with the hyoid. These visceral 
muscles may be divided into two sets according as they are derived 
