. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 6$o Anterior Pectoralis Major ^_^T^>^4^^^^rV—- Brachialis r— Pectoantibrachialis mi Biceps Brachii. Biology of the Vertebrates Clavobrachialis Ectotriceps Epitrochlear H- Meditriceps Fig. 582. Muscles of the front leg of the cat, in cross-sectional view. Proximal cut-surface of the right leg, or distal cut-surface of the left. (From Sayles, Manual for Comparative Anatomy, copyright 1938, by permission of The Macmillan Company, publishers.) V. EMBRYOLOGY
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 6$o Anterior Pectoralis Major ^_^T^>^4^^^^rV—- Brachialis r— Pectoantibrachialis mi Biceps Brachii. Biology of the Vertebrates Clavobrachialis Ectotriceps Epitrochlear H- Meditriceps Fig. 582. Muscles of the front leg of the cat, in cross-sectional view. Proximal cut-surface of the right leg, or distal cut-surface of the left. (From Sayles, Manual for Comparative Anatomy, copyright 1938, by permission of The Macmillan Company, publishers.) V. EMBRYOLOGY OF MUSCLES When mesoderm enters the the scene in vertebrate development, there is much more of it along the dorsal side of the embryo, epimerically, than on the ventral side, hypomerically (Figs. 115 and 116). This distribution is not true of invertebrates, such as annelid worms, in which the mesoderm is about equally distributed all around the body. The reason for the excess of mesoderm along either side of the notochordal level in vertebrates is that this region, after giving off dermatomes and sclerotomes, becomes the myo- tomes, or muscle plates, from which nearly all of the striated muscles of the body are derived. While the major parts of the myotomes remain alongside the developing vertebral column, portions grow ventrally into the region be- tween the parietal mesoderm of the hypomere and the integument until only a thin sheet of connective tissue, the ventral septum, lies between the ventral ends of the myotomes derived from opposite sides of the body. During these embryonic changes the muscle cells, originating in the epi- meric myotome, become rearranged so that their long axes come to parallel the long axis of the body, while between the myotome masses are developed mesenchyme partitions of connective tissue, myocommata, to which the muscle fibers are primarily attached. The end result, as well shown in amphi- oxus (Fig. 13), is a series of <-shaped muscle p
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