Funiculus Cuneatus (Figs. 125 and r33) .—It is separated from the posterior median fissure by the gracile bundle and is the continuation of the ascending postero-lateral column (Burdach's column) of the spinal cord. It ends about the cells of the nucleus funiculi cuneati and accessory nucleus funiculi cuneati, which form the cuneate tubercle seen on the surface. The fibers of the funiculus cuneatus are ascending branches of the posterior roots of the spinal nerves. The nerves contributing to this column are the cervical and the six or eightupper thoracic. The funiculi gracilis and cuneatus carry to the nuclei of these columns common sensations belonging to the tactile and muscular senses. Interference with these tracts produces ataxia.
Spinal Tract of the Trigeminal Nerve (tractus spinalis nervi trigemini, Figs. 123 and i33).—It forms a narrow strip of the posterior surface of the medulla which is broadest near the restiform body and tapers downward toward the spinal cord. It is composed of the descending fibers from the sensory root of the trigeminal nerve: the sensory fibers of this nerve on enter ing the pons divide T-like into an ascending and a descending branch and the descending branches form the spinal tract of the nerve, which for a short distance is visible on the surface of the medulla. This tract is continued through two segments in the spinal cord. The nucleus of the spinal tract of the trigeminal nerve over which it runs and in which it terminates is but the continuation of the gelatinous substance of the posterior columna of gray matter in the cord; in the upper medulla it is situated ventro-medial to the restiform body. The nucleus produces a slight eminence below the level of the clava called the tuberculum cinereum.
The dorsal fasciculus of Flechsig (fasciculus spino-cerebellaris dorsalis, Figs. 13I and 132) in the lower medulla crosses the posterior lateral groove and the spinal tract of the fifth nerve, going from the lateral column of the cord to the pos terior area of the medulla; it then ascends to form a consider able part of the restiform body. It takes its origin from the nucleus dorsalis (Clarki) in the spinal cord. It ends, very largely on the opposite side, in the cortex of the superior cere bellar worm. The dorsal spino-cerebellar fasciculus is a vis ceral afferent tract as its origin in the visceral terminal nucleus of the spinal cord indicates. It is concerned, therefore, with the production of the sympathetic reflexes.
Restiform Body (corpus restiforme).—In the upper medulla forming the lateral part of each posterior area is a large rounded bundle of fibers called the restiform body (Figs. 123,124 and 133). It is the largest bundle in the medulla and joins it to the cerebellum. The restiform body may be divided into a lateral and a medial part. The lateral part contains the dorsal spino cerebellar fasciculus, the external arcuate fibers, the olivo-cere bellar fibers, and the reticulo-cerebellar bundle. The medial part is made up of the direct sensory cerebellar fibers from nerve roots—especially from the trigeminal and vestibular nerves, the nucleo-cerebellar fibers from the terminal nuclei of the medulla, and the fastigio-bulbar bundle of the cerebello tegmental tract. The last tract mentioned is a descending tract, all others of the restiform body are ascending tracts.
The restiform body is inclosed between the vestibular and cochlear roots of the auditory nerve (eighth) (Fig. 119). Ventral to it and between the roots is the ventral part of the cochlear nucleus; on its lateral surface and among the fibers of the lateral root is the dorsal or lateral part of the same nucleus. The vestibular chief dorso-medial nucleus (Schwalbe), the dorso-lateral (Deiters), the superior (Flechsig and Bechterew) and the nucleus of the descending root are situated dorsal and medial to the restiform body.
The restiform body is partly invested by the corpus ponto bulbare discovered by Essick. The ponto-bulbar body is the tail of the pontine migration, the cells that lagged behind in the formation of nucleus pontis. Its position is revealed by the fasciculus obliquus which originates from the cell-bodies of the nucleus ponto-bulbaris. The ponto-bulbar body is a very slender chain of neurones extending from the tnnia of the fourth ven tricle, caudal to the acustic tubercle, obliquely forward between the glossopharyngeal and acustic nerves and then upward between the facial and intermediate nerves into the pons. Having crossed the ponto-medullary groove it continues with the fasciculus obliquus almost to the root of the trigeminal nerve. Sometimes the inferior extremity of the body is a thick "tongue-shaped mass" visible to the naked eye; more often it is thinly spread over the restiform body and is visible only with the microscope. The fasciculus circum-olivaris pyramidis terminates in the nucleus ponto-bulbaris and the fasciculus obliques pontis originates therein.
Tractus Solitarius (Figs. 123 and solitary tract is a small round bundle imbeded in the lateral part of the ventricular gray matter. In Weigert-Pal sections of the upper medulla it is clearly visible to the naked eye. It is formed by the sensory root of the nervus intermedius and the ninth and tenth cerebral nerves. It extends through the nucleus tractus solitarii lateral to the nucleus of the ala cinerea and slightly ventral to it in the upper medulla; but, trending obliquely, it descends dorsal to that nucleus in the lower medulla. Gradu ally approaching the median plane, the two solitary tracts continue through the central gray substance of the lower half of the medulla to its end; Kolliker claims that they reach to the fourth cervical segment but his findings are unconfirmed. The solitary tracts meet at the lower end of the medulla in the nucleus commissuralis of Cajal. In man the solitary tract is made up largely, if not wholly, of taste fibers from the inter mediate and glossopharyngeal nerves. The nucleus of the tract in which its fibers end is the gustatory nucleus of Nageotte whence the gustatory tract of the brain-stem originates.
The solitary tract and the spinal tract of the trigeminal nerve lie on the surface of the medulla in the early embryo, the former being dorsal to the other and close to the rhombic lip. They are alike in composition; each is made up of T branched root fibers. Later both are submerged by the thicken ing of the rhombic lip and the development of the restiform body. Their adult position is thus explained.