HUMAN AND MAMMALIAN. 23 



the border of the hypoglossal nucleus and decussating at the raphe, while others 

 pass backward along the floor of the fourth ventricle. 



In the following paragraphs Clarke has pointed out very clearly some of the 

 conhections established between the tractus intermedio-lateralis' and the respiratory 

 tract above. " It has been seen that the cells of the tracttis intermedio-lateralis are 

 elongated with their processes m a longitudinal direction, and reached by both the 

 posterior and anterior roots of the spinal nerves, and perhaps by the spinal accessory ; 

 that the latter nerve extends forwards to the cells of the anterior cormia, which 

 also send some of their processes longitudinally, and are reached by the posterior 

 roots. Moreover, I have in another memoir shown that, while one portion of 

 the upper roots of the spinal accessory nerve and one portion of the vagus roots 

 proceed intvards to their respective nuclei behind the canal, other portions of hoth 

 hend foi'wards to the vesictdar networh into lohich the anterior oornu has hecome 

 resolved. Again, I have shown, ia the same memoir, that some of the roots of the 

 trifacial nerve descend longitudinally through the caput cornu, between the transverse 

 roots of the vagus ; in which course they are probably brought into connection with 

 the respiratory centres, and perhaps also, like the vagus, with the anterior gray 

 substance of the medulla. These extensive and intimate connections seem to afl^ord 

 an explanation of the mechanism by which impressions made on the vagus and on 

 the incident fibres of the trifacial and spinal nerves, may caU into action the whole 

 class of respiratory muscles ; and if the tract which I have just described in the 

 upper part of the cervical region be continuous, as it probably is, with the tractiLs 

 intermedio-lateralis, Avhich is reached by the dorsal nerves supplying the intercostal 

 and other respiratory muscles of the trunk, the explanation in question wiU be 

 stiU more complete."^ If to these facts, all of which I have had abundant oppor- 

 tunity to confirm most thoroughly, we add the connections pointed out above of the 

 vagal and spi^ial accessory nuclei with the longitudinal colu7nns, which are un- 

 doubtedly continuous with the longitudinal fascicidi in the spinal cord separating 

 the cervix and caput cornu, and standing in close connection with the cells of the 

 tractus intermedio-lateralis, from the upward extension of which tract the spinal 

 accessory and vagal nuclei themselves were shown to be partially formed, we have a 

 series of very extensive and highly interesting connections brought about, the 

 physiological importance of which is at once obvious, though it does not fall within 

 the province of the present commimication to do anything more than simply to call 

 attention to them. 



My own observations thoroughly confirm all the important facts pointed out by 

 Clarke and Schroder van der Ivolk, only diifering from the latter in some of the 

 minor details. The main point, however, I consider completely established, that 

 the respiratory centres are brought into connection with descending fibres from 

 the trifacial, forming together a system of descending longitudinal fasciculi connected 

 with columns of cells, continuous with those in the cervical and dorsal regions of the 

 spinal cord, and thus connected with both anterior and posterior cornua, serving 

 to bring into action a series of movements, both direct and reflex, the importance 

 of which can hardly be over-estimated. 



» Philos. Transactions, 1859, 451. 



