266 The Nerves and Muscles of the Leg 
of the skeleton is marked by condensation of tissue, scleroblastema, to 
form the anlage of the skeleton of the foot, leg, thigh and hip girdle. 
About the scleroblastema is a myogenous zone, the myoblastema, com- 
posed of a slightly less dense tissue. In Embryo CIX, length 11 mm., 
this zone is best marked in the region of the hip (Plate II, Fig. 2). It is 
not clearly defined in the foot region. Between the myoblastema and the 
ectoderm lies a zone of less condensed tissue, the dermoblastema. 
The chief nerves of the limb extend into the myoblastema. This is 
not a homogeneous layer. On the contrary from the time of its forma- 
tion regions which represent the anlages of muscles or groups of muscles 
may be more or less clearly distinguished from regions which represent 
intermuscular spaces. In Plate III, Figs. 1 and 2, an attempt has been 
made to outline the muscle masses which represent the anlages of future 
muscle groups in Embryo CIX, length 11 mm. It is impossible to do 
this with exactness because the various regions are indefinitely bounded. 
In this embryo the pelvic portion of the skeleton consists of a central 
region continuous with the head of the femur. From this central ace- 
tabular portion spring iliac, ischial and pubic processes, The femur is 
short and thick. The tibia and fibula are fairly definitely outlined, the 
foot-plate less definitely so. 
The main nerve trunks have grown for a considerable distance into the 
limb. From them several of the chief muscular and cutaneous branches 
have sprung. The figures show these branches fairly well. In addition 
to the intrinsic nerves of the limb the anterior and posterior border 
nerves are also represented. 
In Fig. 1 it may be seen that the myotomes in the region of the body 
wall have fused to form the anlage of the abdominal musculature. The 
lower margin of this extends distally about to the 21st spinal (1st lum- 
bar) nerve. In Fig. E, Plate V of the article by Bardeen and Lewis, 
o1, it is represented slightly too short. From the ventro-posterior ex- 
tremity of the abdominal musculature a somewhat indefinitely differenti- 
ated band of tissue may be followed to the pubic process of the pelvic 
girdle. 
A slight communicating branch connects the twelfth thoracic with 
the first lumbar nerve. The main portion of this latter nerve extends 
forward on the internal surface of the distal margin of the anlage of 
the abdominal musculature and gives off a lateral, “iliac,” branch. 
Ventrally the nerve divides into branches which represent the hypogastric 
and inguinal nerves. The 1st lumbar nerve also gives off a branch which 
passes to the lumbar plexus. 
