TRANSVERSE SECTIONS OF EMBRYO OF 12 MM. 



185 



is distributed entirely within the medullary wall, while another portion passes 

 out to form ventral roots, one of which, A^. 12, forming part of the hypoglossal 



L.R.I I. 



N. 12. 



Fig. 116. — Pig, 12.0 mm. Transverse Series 5, Section 249. 

 Car. in. Internal carotid artery. cl.I, First or auditory gill cleft. D. Z, Dorsal zone of spinal cord. Ec, 

 Ectoderm. H, Anlage of cerebral hemisphere. Jug, Jugular vein. Jug. in. Internal jugular vein. 

 L, Lens. L.R.ii, Lateral root of the eleventh nerve. L. V, Lateral ventricle. Mx.in, Inferior max- 

 illary nerve. JV.y, Facial nerve. N.g.petr, Petrosal ganglion of the ninth nerve. N.io.ii, United 

 vagus and spinal accessory nerve. N.12, Hypoglossal nerve. Op, Stalk of the optic evagination. 

 Ph, Pharynx. Ret, Retina. V.Z, Ventral zone of spinal cord. X 22 diams. 



nerve, is shown in the figure. A third portion of the neuraxons, at least in the 

 upper cervical region, as also in the medulla oblongata, passes out to form the 



