124 THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



with its geniculate ganglion and its superficial petrosal, chorda tympani and facial 

 branches; (8) the n. acusticus, sensory, arising cranial to the otocyst, with its 

 acustic ganglion and sensory fibers to the internal ear; (9) caudal to the otocyst 

 the n. glossopharyngeus, mixed, with its superior and petrosal ganglia; (10) 

 the' vagus, sensory, with its jugular and nodose ganglia; (n) accompanying the 

 vagus the motor fibers of the spinal accessory which take origin between the 

 jugular and sixth cervical ganglia from the lateral wall of the spinal cord and 

 myelencephalon; the internal branch of the n. accessorius accompanies the vagus; 

 the external branch leaves it between the jugular and nodose ganglia and supplies 

 the sternocleidomastoid and trapezius muscles; (12) the n. hypoglossus, motor, 

 arising by five or six fascicles from the ventral wall of the myelencephalon, its 

 trunk passing lateral to the nodose ganglion and supplying the muscles of the 

 tongue. 



From the jugular ganglion of the vagus extends a nodular chain of ganglion cells. These 

 have been interpreted as accessory vagus ganglia. They may, however, be continuous with 

 Froriep's ganglion which sends sensory fibers to the n. hypoglossus. In pig embryos of 15 to 

 16 mm. this chain is frequently divided into four or five ganglionic masses, of which occasionally 

 two or three (including Froriep's ganglion) may send fibers to the root fascicles of the hypo- 

 glossal nerve. Such a condition is shown in Fig. 116. 



Spinal Nerves. These have each their spinal ganglion, from which the dorsal 

 root fibers are developed (Figs. 115 and 131). The motor fibers take origin from 

 the ventral cells of the neural tube and form the ventral roots which join the 

 dorsal roots in the nerve trunk. 



In Fig. 115 the heart with its right atrium and ventricle, the dorsal and ven- 

 tral lobes of the liver, and the large mesonephros are prominent. Dorsal, and 

 somewhat caudal to the atrium, is the anlage of the right lung. The septum 

 transversum extends between the heart and the liver. 



Pharynx and Its Derivatives. — Dorsally the anterior lobe of the hypophysis 

 is long and forks at its end (Figs. 117 and 118). In the floor of the pharynx are 

 the anlages of the tongue and epiglottis (Fig. 151 A). From each mandibular arch 

 arises an elongated thickening which extends caudal to the second arch. Be- 

 tween, and fused to these thickenings, is the triangular tuberculum impar. The 

 opening of the thyreoid duct between the tuberculum impar and the second arch 

 is early obliterated. A median ridge, or copula, between the second arches con- 

 nects the tuberculum impar with the epiglottis, which seems to develop from the 

 bases of the third and fourth branchial arches. On either side of the slit-like 

 glottis are the arytenoid folds of the larynx. (For the development of the tongue, 



