Warren Harmon Lewis 16B 



■the carpus, and as the metacarpal V continues from it more tlian the 

 unciform tlie whole hand has a peculiar bend toward the ulnar side. 

 From the carpus five masses of condensed tissue project. They shade off 

 into the surrounding mcsenchyma which fills the distal end of the arm. 

 The condition of these finger masses corresponds to the condition of the 

 hand-plate in CLXIII. There is not the sliglitest indication of segmen- 

 tation into metacarpals and phalanges. The radial of the five projec- 

 tions probably consists of both trapezium and metacarpal I, which have 

 not yet shown signs of separate centers of condensation. 



The Musculae System. — The muscle plate system has become differ- 

 entiated into several muscles, namely, the deep dorsal muscles, the inter- 

 costals, the abdominal muscles and the deep ventral neck muscles. 



The infrahyoid muscles correspond in position and nerve supply with 

 the infrahyoid premuscle mass of the preceding stage. They extend 

 nearly to the region where the median end of the clavicle will eventually 

 extend. 



The trapezius muscle has extended posteriorly to the level of the fifth 

 cervical vertebra. Its posterior end lies near to the lateral surface of 

 the body and is connected to the tips of the neural processes as far 

 posteriorly as the second thoracic vertebra by a considerable interval of 

 fascia. As the muscle passes anteriorly it lies deeper and deeper from 

 the surface, being separated from it by the platysma and facial muscles. 

 Its ventral border is free from attachment to the scapula and clavicle. 

 At the level of the second cervical vertebra it is joined by the stemo- 

 mastoid muscle, which has ascended from the more ventral neck region. 

 The nerve supply is as in the adult. 



The rhomboid mass lies in the region of the Y and A^I cervical verte- 

 brae. It connects with the fascia passing to the dorsal tips of the neural 

 processes but has no scapular attachment. A branch of the fifth cervical 

 nerve supplies it. 



The levator scapula; and serratus anterior muscles form a continuous 

 fibrillated mass, extending from the first cervical vertebra to the ninth 

 rib. It occupies much the same position that its premuscle mass did 

 in embryo CLXIII except that the posterior end now extends to the 

 ninth rib. Digitations go to all the cervical transverse processes and 

 to each of the anterior nine ribs. The anterior and posterior digita- 

 tions are very slender and contain but few fibers. The thickest part of 

 the- muscle lies in the scapular region. There is no scapular attachment. 

 The ventral edge of the muscle lies at about the same level as the dorsal 

 edge of the scapula but in a more median plane. Branches from the 

 second to the seventh cervical nerves supply the muscle. The first three 

 13 



