PLATE VI. 

 Figure F. Mag-nification about 10 d. 



Drawing- from a reconstruction of Embryo XXII; length, 20 mm.; age, 

 about 7 weeks (see also Figs. G, H and I). From the arm, leg, body-wall, 

 and the adjacent dorsal region the ectoderm and the superficial tissues have 

 been removed. The muscles and nerves of the body-wall may be recognized 

 readily from their likeness to adult structures. The shoulder muscles and 

 the brachialis and triceps muscles of the upper arm are likewise plain. In 

 the forearm the following muscles may be distinguished from above down- 

 wards: brachio-radialis, extensor carpi radialis longus et brevis, abductor 

 pollicis longus, extensor pollicis brevis, extenso;r pollicis longus and ex- 

 tensor indicis proprius, extensor digitorura communis, extensor carpi 

 ulnaris, and flexor carpi ulnaris; and in the hand the abductor minimi 

 digiti. Branches from the circumflex and radial nerves may be seen. 



In the posterior limb the sartorius and the extensor muscles (the vastus 

 internus, rectus and vastus externus) may be seen above the femur. Be- 

 tween the femur and ilium the tensor vaginae femoris and the gluteus 

 minimus, medius and maximus muscles may be seen. The biceps curves 

 below the knee-joint. In the leg the tibialis anticus, extensor hallucis 

 longus, extensor digitorum communis, and peroneus tertius muscles may be 

 distinguished, and below the last the peroneal muscles. The middle and 

 lateral cutaneous nerves lie over the thigh; the long saphenus, musculo- 

 cutaneous and lateral saphenus lie exposed in the region of the leg and foot. 



The perichondrium has been dissected away from the phalanges of the 

 hand, leaving the cartilaginous cores visible. In the leg and foot the con- 

 densed mesenchyme or perichondrium surrounding the cartilages has been 

 left intact. 



