THE STUDY OF CHICK EMBRYOS 



Ectoderm 



1. Epidermis and its deriva- A 



tives (hair, nails, glands) . i . 



2. Conjunctiva and lens of 2. 



eye. 3- 



3. Sensory epithelia of or- 4. 



gans of special sense. 5. 



4. Epithelium of mouth, 



enamel of teeth, oral 6. 

 glands. Hypophysis. 



5. Epithelium of anus. 



6. Male urethra (distad). B. 



7. Epithelium of amnion and i. 



chorion. 2. 



8. Nervous, neuroglia, and 3. 



chromaffin cells of nerv- 

 ous system. 

 9 Smooth muscle of sweat 4. 



glands and of iris. 

 10. Notochord. =5. 



Mesoderm 



Mesothelium. i. 



Pericardium. 



Pleura. 2. 



Peritoneum. 3. 



Serous layer of intestine. 4. 

 Epithelium of most of 



urogenital organs. 

 Striated muscle. 



1. Skeletal. 



2. Cardiac. 



Mesenchyme. 5. 



Blood cells. 



Bone marrow. 

 Endothelium of blood 

 vessels and lymphatics. 



Entodcrm 



Epithelium of digestive 

 tract. 

 Liver. 

 Pancreas. 

 Epithelium of pharynx. 



Eustachian tube. 



Tonsils. 



Thymus. 



Thyreoid. 



Parathyreoids. 

 Epithelium of respiratory 

 tract. 



Larynx. 



Trachea. 



Lungs. 



Lymphoid organs and 

 suprarenal cortex. 

 Supporting tissues. 

 (Connective tissue, car- 

 tilage and bone. 

 Smooth muscle. 



6. Epithelium of most of 

 bladder, of female ure- 

 thra, male prostatic ure- 

 thra and prostate. 



7. Notochord. 



CHICK EMBRYO OF TWENTY-SEVEN SEGMENTS (FIFTY HOURS) 



This embryo, of nearly- fifty hours' incubation, lies in" the center of 

 the vascular area and is peculiar in that the head is twisted 90 to the 

 right. In a dorsal view, therefore, one sees the right side of the head but 

 the dorsal side of the body. In the region of the mid-brain is a very marked 

 bend, the cephalic flexure. Below the head, and ventral in position, lies 

 the tubular heart, now bent in the form of a letter S. Dorsal to the heart, 

 in the region of the pharynx, three transverse grooves or slits may be seen. 

 These are the branchial grooves, or gill slits. The head of the embryo is 

 now covered by a double fold of the somatopleure, the hsad fold of the 

 amnion. It envelops the head like a veil. Caudally, a fold and opacity 

 mark the position of the tail bud, from which develops the caudal end of 

 the body. The curved fold embracing this is the tail fold of the amnion, 

 which will eventually meet the head fold and completely envelop the 

 embryo. 



Central Nervous System and Sense Organs (Fig. 57). Cephalad, 

 the neural tube is divided by constrictions into four vesicles. The fore- 

 brain of the previous stage is now subdivided into two regions, the telen- 

 cephalon and diencephalon. The cephalic flexure has been established 



