The following cranial nerves arise from the medulla oblongata (Fig. 138). The twelfth nerve (_XII_) (=N. hypoglossus=) arises by ten or fifteen rootlets from the ventral surface of the medulla oblongata in the anterior lateral fissure (_r_) opposite the caudal portion of the area elliptica (_n_). The eleventh cranial nerve (_XI_) (=N. accessorius=) arises by numerous rootlets from the lateral surface of the medulla oblongata and of the spinal cord as far caudad as the sixth or seventh cervical nerve. These rootlets join to form a nerve which enters the cranium through the foramen magnum and is closely associated at its point of exit with the glossopharyngeal (_IX_) and vagus (_X_) nerves. The line of origin on the medulla passes between the dorsal and ventral roots of the cervical nerves and is along the middle of the lateral white funiculi. The tenth cranial nerve (_X_) (=N. vagus=) arises by about eighteen very delicate rootlets from the surface of the area ovalis. The rootlets are divided into a dorsal and a ventral series. The dorsal series (about twelve) arise in the groove which separates the fasciculus cuneatus medialis from the fasciculus cuneatus lateralis. The ventral series arise somewhat ventrad of this groove. These rootlets are to be distinguished from those of the ninth nerve by their smaller size. The ninth cranial nerve (_IX_) (=N. glossopharyngeus=) arises from the area ovalis from a line craniad of the dorsal line of origin of the vagus roots (_X_) and between these and those of the auditory (_VIII_). It arises by a number of rootlets which are larger than those of the vagus (_X_), with which this nerve is closely associated. The eighth cranial nerve (_VIII_) (=N. acusticus=) appears at the lateral end of the trapezium (_l_). It arises from an elevation (Fig. 141, _i_) which is continued dorsomediad along the cranial border of the area ovalis. The seventh cranial nerve (_VII_) (=N. facialis=) leaves the lateral border of the trapezium (_l_) near its cranial edge, between the fifth and eighth nerves. It is much smaller than the eighth nerve. The sixth cranial nerve (_VI_) (=N. abducens=) arises by about six bundles from the groove between the pyramids and the trapezii and passes craniad. 2. _Metencephalon._--The metencephalon includes the =pons= and the =cerebellum=. The =pons= (Fig. 138, _i_) is a mass of transverse fibres which forms the ventral and cranial part of the primitive hindbrain. It is a modification of the latter brought about by the development of the cerebellum, and the degree of its development is in direct ratio to that of the cerebellar and cerebral hemispheres. The pons forms a projecting mass of fibres which is marked by a median longitudinal groove, the =sulcus basilaris= (_j_), which indicates the course of the basilar artery (Fig. 121, _c_). Laterad the fibres of the pons converge somewhat and turning dorsad disappear in the cerebellum, forming the =brachia pontis= (Fig. 141, _l_).