i33o A MANUAL OF ANATOMY 



of the cord . It commences in the lower part of the thoracic region, 

 and superiorly it traverses the lower part of the medulla oblongata 

 on its lateral aspect, after which it enters the restiform body, by 

 which it is conducted to the vermis of the cerebellum. Its fibres 

 are usually regarded as being derived from the posterior vesicular 

 column of Clarke. 



The ventral spino-cerebellar tract, or tract of Gowers [fasciculus 

 antero-lateralis superficialis B.), is situated chiefly in the lateral 

 column, in front of the dorsal cerebellar tract close to the outer 

 surface of the cord . It is comma-shaped in section, its dorsal part 

 being broad, but, as it extends forwards between the funiculi of the 

 ventral nerve-roots, it tapers and enters the ventral column super- 

 ficially. It commences near the lumbar region of the cord. 

 Superiorly it extends through the medulla oblongata and pons, 

 and thereafter passes along the superior cerebellar peduncle into 

 the cerebellum, terminating in the vermis. It therefore takes an 

 indirect course as compared with that of the dorsal spino-cerebellar 

 tract. Its fibres are usually regarded as being derived from the 

 posterior vesicular colimin of Clarke. The ventral spino-cerebellar 

 tract contains the spino-thalamic and spino-tectal tracts. 



The spino-thalamic tract consists of fibres which arise as the 

 axons of cells of the dorsal grey comu, around which cells the fibres 

 of the dorsal nerve-roots have terminated. The spino-thalamic 

 fibres cross to the opposite side in the ventral or white commissure, 

 thus giving rise to a spinal inferior sensory decussation or spino- 

 thalamic decussation, as distinguished from the superior sensory 

 decussation in the bulb, called the decussation of the fillets, which is 

 produced by the deep arcuate fibres which arise from the cells of the 

 nucleus gracilis and nucleus cuneatus. The spino-thalamic fibres, 

 having crossed in the ventral white commissure, ascend in the 

 tract of Gowers, and, after traversing the bulb and pons, they 

 terminate in the optic thalamus of the side to which they have 

 crossed as a cell-station. It is important to note that there are 

 two sensory decussations — lower or spinal, and upper or bulbar. 

 In unilateral lesions of the spinal cord there would only be 

 partial anaesthesia on the opposite side; whereas in unilateral 

 lesions of the bulb, involving both the fillet-fibres and the spino-, 

 thalamic fibres, there would be complete anaesthesia on the opposite ' 

 side. 



The spino-tectal tract is also an ascending tract. Its fibres are 

 connected with the cells of the ventral comu of grey matter. Thej 

 ascend in conjunction with the tract of Gowers and pass througi 

 the formatio reticularis of the bulb and pons. Thereafter tliej 

 decussate with those of the opposite side, forming the fountain^ 

 decussation of Meynert, which lies between the two red nuclei, tc 

 which nuclei the spino-tectal fibres furnish collaterals. After the 

 decussation the fibres of either side pass to the corresponding 

 superior colliculus of the corpora quadrigemina. 



