DEVELOPMENT OF THE STERNUM 



97 



ma 









v-s* 



Fig. 3 Pig, 20 mm. TransveiTse section 10 sections anterior to level of 1st rib, 

 right side; mxt, median plane of body; s6, sternal band; ma, median portion of 

 anlage; pw, pectoral muscle. X 60. 



Fig. 4 Pig, 18 mm. long. Transverse section at level of 3d rib, right side; 

 tB, ventral extremity of 3d rib; sh, sternal band. X 200. 



We find the next stage in an embryo 18 mm. long. Here the 

 pericardial cavity and the heart are well forward in the neck, and 

 the anterior extremities of the sternal bands are widely separated 

 thereby. There is no evidence whatever of the median portion 



