THE ANATOMY OF A SIX MM. PIG EMBRYO 93 



enlargements along this neural crest represent developing cerebral and spinal 

 ganglia. They are in order the superior or root ganglion of the glossopharyngeal 

 nerve with its distal petrosal ganglion; the ganghon jugulare and distal ganglion 

 nodosum of the vagus nerve; the ganghonic crest and the proximal portion of the 

 spinal accessory nerve; and the anlage of Froriep's ganglion, an enlargement on the 

 neural crest just cranial to the first cervical ganghon. Between the vagus 

 and Froriep's ganghon may be seen the numerous root fascicles of the hypoglossal 

 nerve, which take their origin along the ventro-lateral wall of the myelencephalon 

 and unite to form a single trunk. The posterior roots of the spinal ganglia are 

 very short; their anterior or ventral roots are not shown. 



The position of the heart with its ventricle, atrium, and sinus venosus are 

 shown. The liver is divided into a small dorsal and a large ventral lobe. The 

 fore-gut emerges from between the hver lobes and curves ventrad to the yolk 

 stalk and sac. The hind-gut is partly hidden by the fore-gut; it make a U- 

 shaped bend from the yolk stalk to the caudal region. The gut is attached to 

 the dorsal body wall by a double layer of splanchnic mesoderm which forms the 

 mesentery. The long, slender mesonephros hes ventral to the- spinal cord and 

 curves caudad from a point opposite the eighth cervical ganglion to the tail re- 

 gion. The cranial third of the mesonephros is widest arid its size diminishes 

 tailwards. Between the yolk sac and the tail the allantois is seen, its stalk 

 curving around from the ventral side of the tail region. 



Digestive Canal. — The arrangement of the viscera may be seen in median 

 sagittal and ventral dissections (Figs. 96 and 97), also in the reconstruction 

 shown in Fig. 105. The mouth lies between the mandible, the median fronto- 

 nasal process of the head, and the maxillary processes at the sides. The divertic- 

 ulum of the hypophysis (Rathke's pocket) , flattened cephalo-caudad and expanded 

 laterad, extends along the ventral wall of the fore-brain (Fig. 105). Near its 

 distal end, the wall of the brain is thickened and later the posterior lobe of the 

 hypophysis will develop froru the brain wall at this point. 



The pharynx is flattened dorso-ventrally and is widest near the mouth. Its 

 lateral dimension narrows caudad, and opposite the third branchial arch it makes 

 an abrupt bend, a bend which corresponds to the cervical flexure of the embryo's 

 body (Figs. 104 and 105). In the roof of the pharynx, just caudal to Rathke's 

 pocket, is the somewhat cone-shaped pouch known as Seessel's pocket, which may 

 be interpreted as the blind cephalic end of the fore-gut. The lateral and ven- 

 tral walls of the pharynx and oral cavity are shown in Fig. 98. Of the four arches 

 the mandibular is the largest and a groove partly separates the processes of the 



