In the formation of membrane bone, individual shafts of bone, known as trabeculae, are laid down (see Plate 1-10). Trabeculae increase in length and thickness and join each other at…
SKELETAL MUSCLE INNERVATION The establishment of neural contacts with developing skeletal muscle fibers is a critical developmental stage. The contacts enhance muscle development and are important for the complete differentiation…
At 6 weeks, the flexed limbs have not yet rotated out of their primary position (see Plate 1-8). Because the upper and lower limbs later undergo opposite rotations to reach…
In humans, a striated cloacal sphincter muscle and levator ani muscle (pelvic diaphragm) arise from the third sacral to the first coccygeal myotomic hypomeres and are well developed by the…
After the transverse processes appear, the ribs form in the sclerotomal tissue that extends by differentiation into the ventral portions of the original clefts between the somites. The maximum development…
2. Portions of successive myotomes commonly fuse to form a composite single muscle (the erector spinae and rectus abdominis muscles). The latter is formed by the fusion of the ventral…
The cells of the myotome, the mononucleated myoblasts, elongate in a direction parallel to the long axis of the embryo (see Plate 1-17) and undergo repeated mitotic divisions, subsequently fusing…
During vertebrate evolution, the head underwent changes related to the development of the special senses. The anterior end of the nerve cord became a brain, and the nerves passing to…
The dense concentration in cardiac muscle of orderly arrangements of interdigitating actin and myosin molecules, which could synchronously slide across each other throughout the atrial or ventricular muscle, resulted in…
The branchial arch skeleton is derived from the embryonic counterparts of the gill arches that support the mouth and pharynx of present-day adult fish and tailed amphibians. The most primitive…
