EMBRYO OF 24 MM. 267 



vertebral ligaments. The cartilage of the body of the vertebra continues past the 

 intervertebral expansion of the notochordal cavity, but the external portion of 

 the chondrostyle opposite each such expansion exhibits a modification of its cells, 

 for they have become lengthened out in a direction parallel with the vertebral axis. 

 The tissue thus produced is the anlage of the vertebral ligaments. The mouth 

 and pharynx, Ph, form a narrow cavity, the floor of which is constituted by the 

 tongue, Ton, the tip of which has already become free. The surface of the tongue 

 forms a long arch, at the posterior end of which lies the epiglottis, a projecting 

 fold of tissue which covers the opening of the trachea. The side of the trachea is 

 marked by the longitudinal fold, La, which separates the trachea proper from the 

 upper end of the oesophagus, CE. At the upper end of the oesophagus there is a 

 small dorsal diverticulum. If the reference line (E be followed a short distance 

 past the oesophagus, it will lead to the section of the main aorta. A little lower 

 down is the section of the arch of the aorta, A. Ao. The heart shows chiefly its 

 large ventricle, Ven. The section is not favorable for an exhibition of its struc- 

 ture or for that of the lungs, Lu. It does, however, — since in this part of the 

 embryo the section passes to one side of the median plane, — show the main bron- 

 chus, Bro, coming off from the trachea to the lung, and some of the smaller ento- 

 dermal bronchial branches, bro, in the lung itself. The heart and lung are sepa- 

 rated from the abdominal cavity by the diaphragm, Diaph. It is only to the 

 dorsal part of this diaphragm that the liver, Li, is attached. In earlier stages 

 the liver is connected with the whole of the diaphragm (septum transversum) . We 

 now have a portion of the diaphragm without connection with the liver. Below 

 the liver is the section of the stomach, St, the entoderm of which is cut twice. 

 Below the stomach lies the duodenum, Duo, extending from the dorsal side of the 

 embryo and running toward the umbilicus. At the dorsal end of the duodenum 

 is a group of clusters of darkly stained cells, marking the position of the anlage 

 of the pancreas. Below the duodenum the loops of the intestine. In, are cut re- 

 peatedly. On the dorsal side of these loops is the section of the genital gland, in 

 this specimen, testis, Te. Dorsalwards from the genital gland is the complicated 

 anlage of the suprarenal capsule, Sp. ren, which is really a double organ, having 

 one part derived from the sympathetic nervous system and another from a modi- 

 fication of mesenchymal cells. In a sagittal series the connection of the anlage 

 with the sympathetic nervous chain of the abdomen can be readily made out- 

 In the anlage the nerve-fibers and the sympathetic cells are irregularly distrib- 

 uted, although the cells are more or less grouped together. The sympathetic tissue 

 constitutes the dorsal part of the anlage and gives rise to the so-called medulla of 

 the adult organ. The ventral portion of the anlage, as seen in the section, con- 

 sists of bands or cords of cells separated from one another by venous sinusoids. 



