FIGURES 103 AND 104 



103 Transverse section of ventral part of upper thoracic region in a 12 mm. cat 

 embryo (series 217, slide ^'III, section 21), X 200. 



104 Same, section 29. 



7 Aorta. 



9 Trachea. 



10 Pulmonary artery. 



18 Peritracheal venous plexus. 



22 Vagus. 



