STUDY OF SECTIONS OF EMBRYO OF 24 MM. 337 



the nucleus pulposus of the adult. From each such mass goes off a narrow exten- 

 sion of the notochord, through what is to become the body of the vertebra. Some- 

 times this extension is continuous with the intervertebral portions of the notochord, 

 but more usually it forms a series of isolated fragments, for the notochord in the 

 parts corresponding to the bodies of the vertebrae is already in process of resorption. 

 The diameter of the chondrostyle is nearly uniform in the vertebral region, but 

 is a little smaller in the part corresponding to each body of a vertebra and a little 

 wider in the parts corresponding to the intervertebral ligaments. The cartilage of 

 the body of the vertebra continues past the intervertebral expansion of the noto- 

 chordal 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 intervertebral ligaments. The mouth and pharynx, Ph, form a nar- 

 row 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 longitudi- 

 nal fold, La, which separates the trachea proper from the upper end of the ceso- 

 phagus, (E. At the upper end of the oesophagus there is a small dorsal diverticu- 

 lum. If the reference line (E were continued a short distance past the oesophagus, it 

 would 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 structure 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 bronchus, Bro, coming off from the 

 trachea to the lung, and some of the smaller entodermal bronchial branches, bro, 

 in the lung itself. The heart and lung are separated 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 um- 

 bilicus. At the dorsal end of the duodenum is a group or cluster of darkly stained 

 cells, marking the position of the anlage of the pancreas. Below the duodenum the 

 loops of the intestine, In, are cut repeatedly. On the dorsal side of these loops is 

 the section of the genital gland, in this specimen, testis, Te. Dorsalward 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 modification 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 



