ANATOMY OF THE PONS 123 



oblongata and spinal cord on the one hand with the cerebellum on the other. 

 By a careful inspection of the surface of the medulla it is possible to recognize 

 the source of some of the fibers entering into the composition of the restiform 

 body. The ventral external arcuate fibers can be seen entering it after crossing 

 over the surface of the lateral area; and the dorsal spinocerebellar tract can also 

 be traced into it from a position dorsal to the caudal extremity of the olive. 



At the point where the restiform body begins to turn dorsally toward the 

 cerebellum, it is partly encircled by an elongated transversely placed elevation 

 formed by the ventral and dorsal cochlear nuclei (Figs. 87, 88). This ridge is 

 continuous on the one hand with the cochlear nerve, and on the other with 

 several bundles of fibers which run medialward over the floor of the fourth 

 ventricle and are known as the stria medullares acusticce (Fig. 89). The cochlear 

 nuclei are more prominent in the sheep, while the medullary striae are best seen 

 in the human brain. Just caudal to this ridge there is sometimes seen another, 

 running more obliquely across the restiform body, which is an outlying portion 

 of the pons and has been described by Essick (1907) under the name corpus 

 pontobulbare. 



Nerve Roots. From the surface of the medulla oblongata there emerge in 

 linear order along the posterior lateral sulcus a series of root filaments, which 

 continues the line of the dorsal roots of the spinal nerves. These are the root- 

 lets of the glossopharyngealj vagus and accessory nerves. But unlike the dorsal 

 roots, which are made up of afferent fibers, the spinal accessory nerve contains 

 efferent fibers, while the vagus and glossopharyngeal are mixed nerves. The 

 line of the ventral or motor roots of the spinal nerves is continued in the medulla 

 oblongata by the root filaments of the hypoglossal neroe, which is also composed 

 of motor fibers. The abducens, facial, and acoustic nerves make their exit along 

 the caudal border of the pons in the order named from within outward. The 

 abducens emerges between the pons and the pyramid, the acoustic far lateral- 

 ward in line with the restiform body, and the facial with its sensory root, the 

 nervus intermedius , near the acoustic nerve (Figs. 86-88). 



THE ANATOMY OF THE PONS 



The pons, which is differentiated from the ventral part of the metencephalon, 

 is interposed between the medulla oblongata and the cerebral peduncles and 

 lies ventral to the cerebellum. As seen from the ventral surface, it is formed 

 by a broad transverse band of nerve-fibers, which on either side become aggre- 

 gated into a large rounded strand, the brachium pontis or middle cerebellar 



