LATERAL DISSECTION OF THE VISCERA IOI 



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

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

 nodosum of the vagus nerve; the ganglionic crest and 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 ganglion. Between the 

 vagus and Froriep's ganglion 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 liver lobes and curves ventrad to the yolk- 

 stalk and sac. The hind-gut is partly hidden by the fore-gut; it makes 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 lies 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 and 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. 91 and 92), also in the reconstruction 

 shown in Fig. 100. The mouth lies between the mandible, the median nasal 

 process of the head, and the maxillary processes at the sides. The diverticulum 

 of the hypophysis, flattened cephalo-caudad and expanded laterad, extends along 

 the ventral wall of the fore-brain (Fig. 99). Near its distal end, the wall of the 

 brain is thickened and later the posterior lobe of the hypophysis will develop 

 from the brain wall at this point. 



The pharynx is flattened dorso-ventraUy 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. 99 and 100). 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. 93. Of the four arches 

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

 two sides. Posterior to this groove and extending in the median line to the 



