THE EXITS OF THE CEREBRAL NERVES. 69 



remarkable nerves, wliicli pass to the gullet and stomach, the 

 respiratory and vocal organs, to some parts of the integument 

 of the body, and to the heart. In the Ichtliyopsida they give 

 oiT, in addition, long lateral nerves to the integuments of the 

 sides of the body. In the higher Yertebrata^ these lateral 

 nerves are represented only by small branches distributed 

 chiefly to the occipital region. The ninth and tenth pairs are 

 both motor and sensory in function, and are often so inti- 

 mately connected as to form almost one nerve. 



The eleventh pair (accessorii) are cerebral only by courtesy, 

 as these nerves take their origin from the spinal cord, by 

 roots which issue between the proper anterior and posterior 

 roots of the spinal nerves, and, joining together, form, on 

 each side, a nerve which passes out with the pneumogastric, 

 partly joining it, and partly going to muscles which arise from 

 the head and anterior vertebrae, and are inserted into the pec- 

 toral arch. 



The spinal accessory exists in no Ichthyopsid vertebrate, 

 but is found in all Saurojysida^ with the exception of the 

 Ophidia^ and in the Maminalia. 



The twelfth and last pair {Jiypoglossi) are the motor nerves 

 of the tongue, and of some retractor muscles of the hyoidean 

 apparatus. 



In the Ichtliyopsida the first cervical nerve supplies the 

 distributional area of the hypoglossal ; but in all the abran- 

 chiate Yertebrata there is a hypoglossal, which traverses a 

 foramen in the ex-occipital, though it oftens remains closely 

 connected with the first cervical, and may rather be regarded 

 as a subdivision of that nerve, than as a proper cerebral 

 nerve. 



Thus the nerves arising from the hind-brain, in all the 

 higher Yertehrata, fall into three groups : 1st, a sensori-motor, 

 pre-auditory, set (3d, 4th, 5th, 6th, 7th) ; 2d, the purely sen- 

 sory auditory nerve (8th) ; 3d, the sensori-motor, post-audi- 

 tory, set (9th, 10th, 12th). 



The apertures by which several of these nerves leave the 

 skull, retain a very constant relation to certain elements of 

 the cranium on each side. Thus : 



a. The filaments of the olfactory nerve always leave the 

 crauium between the lamina perpendicularis, or body of the 

 ethmoid, and its lateral or prefrontal portion. 



b. The optic nerve constantly passes out behind the cen- 

 tre of the orbitosphenoid and in front of that of the alisphc 

 uoid. 



