34 ANATOMY OF THE DOMESTIC FOWL 



In sectioning the embryo from before backward, the first sections 

 will pass horizontally through the hindbrain and the midbrain 

 region. Note the parts, including the auditory vesicle. In the 

 first series of sections also locate the ganglia of the pneumogastric, 

 or vagus, the acoustico-facialis, the trigeminus, and the glosso- 

 pharyngeal nerves. Note the notochord and the cardinal veins. 

 After the disappearance of the ear, we observe the midbrain, which, 

 is located at one end of the section, and the cord at the other end. 

 The region between lies just above the pharynx. In the following 

 series study the visceral arches. Note the third pair of cranial, or 

 motor ocular, nerves. This latter nerve springs from the floor of 

 the midbrain. From the ventral prolongation of the floor of the 

 thalamencephalon there arises the infundibulum. The hypophysis 

 is located just beneath the infundibulum. At this stage the hypo- 

 physis appears as a tube to empty into the mouth. This is an in- 

 growth of the oral epithelium. 



In a study of a section through the center of the eye we should 

 observe the lens and optic stalk. This is in the region of the optic 

 chiasm. Note the choroid fissure and the pineal gland, the latter 

 appearing just beyond the eyes. Just forward lies the telencephalon, 

 or rudiments of the cerebral hemispheres. 



In a study of the alimentary tract we note that the mouth is 

 bounded by the mandibular arches. Note the maxillary processes, 

 and the ventral surface of the head. A finger-like diverticulum, 

 extending from the roof of the ruptured double membrane, formerly 

 separating the pharynx from the arches, forms the hypophysis. 

 The great development of the visceral pouches makes the pharynx 

 rather complex. In studying sections horizontally through the 

 pharyngeal region note the various visceral arches and pouches. 

 Note the arteries of the thyroid diverticulum. 



In the series note the changed development of the lung rudiments, 

 the glottis, the esophagus, the trachea, and the bronchi. The bron- 

 chi appear in pairs. Note that the liver has assumed proportions, 

 and that it surrounds the common trunk of the vitelline veins, 

 which it divides into two parts. The sinus venosus lies close to the 

 heart. The ductus venosus is also surrounded by the liver. Above 

 the "tip of the ventricle we note a dilatation which represents the 

 stomach. The hepatic, or bile duct is located immediately behind 

 the stomach. This duct is formed by the fusion of the right and the 

 left duct. Locate, draw, and describe the pancreas; trace the intes- 



