30 Development of the Limbs, Body-wall and Back in Man 



The mnscnlatnre of the back and abdominal walls has a general 

 resemblance to that of the adult. Fig. I shows the musculature of the 

 abdomen and thorax as seen from within, Figs. F and G that of the more 

 superficial layers of the abdomen and thorax, and Fig. H that of the 

 deeper layers of the abdomen and thorax. The dorsal muscles are not 

 clearly shown in any of the figures, but they are divisible into the three 

 distinct groups, the ileo-costal, longissimus dorsi, and spinalis muscles, 

 characteristic of the adult. 



Fig. 26. Skeleton of distal half of Embryo XXII. At the left side the covering 

 of dense embryonic connective tissue is shown, at the right the parts composed of 

 embryonic cartilage, x 10 d. 



The nerves, like the muscles, have a distribution essentially similar to 

 that found in the adult. The figures indicate with sufficient clearness 

 the distribution of the thoraco-abdominal and border nerves. 



The main blood-vessels are those characteristic of the adult. 

 ■ In the posterior limb the skeletal tissue has undergone extensive 

 differentiation. The rudiments of all of the bones of the leg may be 

 seen in the form of cartilage except that the terminal phalanges of the 



