Susanna Phelps Gage 415 



said, duodenmn, in the eoelom canals which lie dorsad of the septum traus- 

 versnm (Fig. 3) ; the caudal end of the eoelom canals opposite the 2d or 

 perhaps the 3d thoracic myotome (13th myotome). 



It seems to me that the most cephalic portion of the pericardial eoelom 

 might be said to be that surrounding the buHuis arteriosus, in which case 

 it would be difficult to decide that it had retreated so far from its oriffi- 

 nal position opposite the ear as Mall has mentioned. 



The specimen and the model show more clearly than any of the draw- 

 ings, the caudal traction of the organs which has taken place while their 

 original cephalic attachment can still be traced. The furrows of the 

 mesentery (Figs. 3, 6, 10, 11) show this more clearly than the varying 

 caliber which indicates the division of the entodermal tube into organs. 

 The furrow, for instance, separating duodenum and yolk sac extends 

 cephalad to the 8th myotome (6th cervical), and the attachments of all 

 the entodermal organs cephalad of it are spread out between this point 

 and the 1st occipital myotome, that is in the neck. From this, it hardly 

 seems correct to say that lung and stomach are really so far cephalad as 

 mentioned by Mall (i. e. in the head). 



Mesoderm. 



General. — The general appearance of the mesodermic tissue is shown 

 in Plate Y, being entirely cellular. The condensations in the nephric 

 region are described below. Other condensation is seen in the limbs, but 

 without clear differentiation into separate masses. Condensation also 

 occurs at the side of the pharynx and markedly so in the floor. This 

 continues uninterruptedly into the thick mesentery surrounding lungs, 

 esophagus, stomach, and intestines (Figs. 2, 3, 6, 10, 11), and in the 

 region of the cloaca joins the condensation around the Wolffian duct and 

 continues into and fills the leg-bud. 



A distinct spindle-shaped condensation of cells occurs ventrad of the 

 eye (Figs. 7,8). 



Myotomes. — Bardeen and Lewis " give the following description : 

 " Length, neck-breach, 4.3 mm. ; age about three weeks. . . . Though 

 more advanced in development than Lr (His), but twenty-seven myo- 

 tomes are present (2o, 8c, lOt, 51, 2s). This has been determined by 

 careful counting of the myotomes in serial sections of the embryo. The 

 base of the arm-bud appears to lie opposite the seventh to the eleventh 

 myotomes. It is, therefore, probable that two occipital myotomes are 

 present. But nine myotomes lie in the area l)otween the arm-bud and the 



" Bardeen, C. R., and Lewis, W. H., Amer. Jour. Anat., I, 1901. 



