MUSCULAR SYSTEM. I31 
different groups. Thus the spinales connect the spinous processes, the 
transversales the transverse processes of the successive vertebrae, 
while the transverso-spinales extend from the transverse process of 
one vertebra to the spinous process of the next. In the higher verte- 
brates the anterior spinalis, connecting the first vertebra with the skull, 
is divided into several rectus capitis muscles. The longissimus 
dorsi group extends from the pelvis to the head, lying on either side in 
the angle between spinous and transverse processes. It may be differen- 
tiated into separate muscles—a longissimus dorsi proper in the lumbar 
region, an ileo-costalis inserted on the dorsal part of the ribs, anda 
longissimus capitis along the side of the neck to the temporal region 
of the skull. 
The muscles which move the appendages are divided into the 
intrinsic, which are located in the limb itself and have their origin 
either from the bones of the limb or from the supporting girdle, and the 
extrinsic, which have their origin on the trunk and are inserted on the 
girdle or the base of the limb. The latter move the limb as a whole, 
my my 
“ev Se 
Fic. 139.—Budding of muscles of appendage from myotomes in Pristiurus, after Rabl 
b, muscle buds; my, myotomes. 
while the intrinsic bend the limb on itself. As would be expected from 
the motions of the fins, the intrinsic muscles are hardly noticeable in the 
fishes, the various movements being accomplished by the extrinsic 
group. These latter are divided into protractors which draw the 
member forward; retractors which pull it back against the body; 
levators which lift it and depressors which pull it down. 
In those vertebrates which are sufficiently known the first traces of the develop- 
ment of the musculature of the appendages are the appearance of two buds (fig. 
139) from the ventral border of a varying number of myotomes in the region of the 
developing limb. These buds proliferate cords of cells which soon lose their 
distinctness and form a blastema from which the intrinsic muscles arise, the 
definitive muscles being innervated by as many spinal nerves as there are contribut- 
ing myotomes. The extrinsic muscles arise directly from the myotomes. 
