No.2.] VENTRAL ABDOMINAL WALLS IN MAN. 353 
transversum,' and its nerve supply indicates that the muscle 
must have arisen from the fourth or fifth cervical myotome or 
both. After the septum transversum has reached its final 
location, to form the diaphragm, muscles arising from the lower 
dorsal myotomes wander into its periphery and these are inner- 
vated by the lower intercostal nerves. In the same way the 
sterno-mastoid and trapezius grow over from the head to the 
shoulder, while the latissimus dorsi and serratus anticus grow 
from the shoulder to the ribs and pelvis. I have already spoken 
of the serratus anticus above, and wish to add a few words about 
the latissimus dorsi. It undoubtedly arises from the seventh and 
eighth cervical myotomes, is soon separated, and free to move. 
It attaches itself first to the humerus and then gradually spreads 
out over the back, attaching itself first to the vertebrae, then 
to the ribs, and finally to the ilium. As the growth takes place 
in this order the shoulder end is the older, and the pelvic end 
the younger, thus accounting for the nerve distribution as shown 
recently by Nussbaum.” In spreading, its fasciculi cross and 
encircle branches from the intercostal and lumbar nerves, thus 
making them perforate this muscle. Other muscles that shift, 
like the deltoid and pectoralis major, are likewise perforated 
but not innervated by nerves foreign to them. 
Sometimes muscles which remain segmental cover metameres 
beyond their nervous supply. Quain’s? Azatomy, in discussing 
the quadratus lumborum and complexus muscles, asserts that this 
indicatesa reduction of the number of nerves, while from the above 
discussion it appears to me that it is not a reduction of nerves 
but an extension of the muscle beyond its original bounds. 
Likewise a complete absence of an important muscle (trape- 
zius), or a group of muscles (facial), is not necessarily to be 
accounted for by a degeneration of the nerve. Anything which 
arrests the development of the muscle in its very earliest stage 
will accomplish absence of the nerve, while a nerve destroyed 
at so early a stage might be replaced by a neighboring nerve 
through anastomoses. 
1 Mall, Journ. of Morph., vol. xii, p. 395, Figs. 30, 41. 
2 Nussbaum, Verhandl. d. Anat. Ges., 1894, p. 179; 1895, p. 26; 1896, p. 64. 
3 Quain’s Anatomy, vol. ii, p. 354. 
