Fig. 13 Photomicrograph of a transverse setion through the ventral cephalic 
region in a 9-mm. embryo of Bufo vulgaris (K. E. C., series B 2, slide 1, section 
115). X 290. si..max. prim., primary maxillary lymph sinus; the spurs of tissue 
projecting into its lumen are the vestiges of the former bands of mesenchyme 
between the lymph channels during the plexus stage of the sinus. Other refer- 
ences as in previous figures. 
Fig. 14 Photomicrograph of a transverse section through the left ventral 
region of the body at the level of the heart in a 7-mm. embryo of Bufo vulgaris 
(K. E. C., series B 27, slide 1, section 178). X 690. cor, wall of the heart; cav. 
pericard., cavum pericardium; ep., epidermis; v. jug. ext. sin., vena jugularis 
externa sinistra; lym., anlage of the pericardial division of the primary maxillary 
sinus. 
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