Nervous System General, 125 



Of the ' Seventh Pair,' the portio dura (or facial nerve), tra- 

 verses the parotid gland in those Mammals in which that gland 

 is well developed. The large development of that part of the 

 'portio mollis ' (or auditory nerve) which supplies the cochlea is 

 characteristic of the Mammalia; in which the posterior division, 

 answering to the main part of the acoustic in lower Yertebrates, 

 is spent upon the vestibule and semicircular canals. 



Of the Eighth Cerebral Nerve j the *glosso-pharyngeal' division 

 is relatively smaller in Mammals than in Birds : it is mainly 

 distributed to the back part of the tongue, and to the pharynx 

 in all members of this Class. The Vagus, or ' pneumogastric 

 division' has, as in the other Yertebrata, the longest course, 

 widest distribution, and most numerous connexions of any 

 of the Cerebral nerves ; but is characterised, in Mammals, by 

 receiving the * accessory ' nerve from a greater extent of the 

 myelon. The * recurrent ' branches of the Yagus are more 

 exclusively distributed to the trachea and larynx, and send 

 a smaller supply of nerves to the oesophagus than in Birds or 

 Reptiles. In most Mammals the Yagus after its exit from 

 the jugular foramen, exhibits a grey enlargement ; but this 

 is less distinctly divided into an upper and lower ganglion 

 than it is in Man. 



The Ninth, or motor nerve of the tongue (hypoglossal) 

 varies in size according to the length of the tongue and the 

 frequency and extent of its muscular motion. In most Mam- 

 mals the filaments of this nerve are collected into two bundles 

 which pass out each by a single precondyloid foramen, but 

 two foramina are occasionally found on each side. 



The Sytnpathetic nerve system is much the same as in Man : 

 it influences the contractile power of blood vessels, the coats of 

 which, in all Mammals, show a considerable plexiform supply 

 therefrom. In all Mammals the parts regarded as * trunks,' or 

 *main cords' of the sympathetic, form a symmetrical pair, 

 extending along the sides of the centrums of the Yertebrao, 

 forw^ard to the basioccipital, and backward to the coccvx. 



