58 H. VON W. SCHULTE 



cleft as is readily seen in the view from the right and above 

 shown in figure 7, and caudad there is a slight nearly transverse 

 depression furrowing the apex of the cardiac loop, associated 

 with an ental ridge which marks the beginning of the septum 

 ventriculorum. 



Fig. 8 Cephalic portion of same model as in figures 6 and 7, ental view. /, 

 Ridge representing middle cardiac plate; 2, fundus of right bulbo-ventricular 

 sulcus; 3, fundus of left Indbo-ventricular sulcus; 4, interior of bulbus; 5, atrial 

 region; 6, dorsal mesocardiiun. 



The changes that have supervened to transform this heart in 

 the period between appearance of the twelfth and fourteen pairs 

 of somites are easily appreciated on the comparison of the fig- 

 ures (figs. 4 and 7). The most striking changes affect the shoul- 

 ders of the mantles, that of the left side is greatly elevated, that 

 of the right correspondingly depressed. This entails a deep- 

 ening of the left bulbo-ventricular sulcus and an opening out on 



