THE CRANIAL OR ENCEPHALIC NERVES. 739 



the prolongation of the line of insertion of the inferior spinal roots, by a 

 dozen converging filaments. These traverse the dura mater in two or 

 three bundles, which enter -the condyloid foramen of the occipital bone 

 where they unite to form a single cord. The hypoglossal has also a 

 ganglionic root which Toussaint constantly found in the Ass, Mule, Ox, 

 and Dog, and which had been previously seen by Meyer and Vulpian! 

 The ganglion of the hypoglossal in the Horse is fusiform, and the size of 

 a small lentil (Fig. 338, o'). It is sometimes absent. 



Distribution. — The hypoglossal nerve thus constituted, immediately after 

 its departure from the condyloid foramen, communicates with the first 

 cervical pair by means of a transverse ramuscule ; it then passes between 

 the spinal accessory and pneumogastric nerves, descends on the external 

 face of the guttural pouch, where it is connected with the superior cervical 

 ganglion of the sympathetic by numerous filaments, which in great part form 

 the plexiform network called the " guttural plexus." The nerve afterwards 

 crosses to the outside of the external carotid artery, in proceeding forward 

 and downward on the side of the pharynx and larynx, receiving at that 

 point a slender ramuscule from the first cervical ; it then passes within the 

 inferior extremity of the stylo-hyoid muscle and the glosso-faciai artery, 

 which it crosses very obliquely, is prolonged between the mylo-hyoid and 

 hyo-glossus brevis muscles, sends numerous small filaments to the latter and 

 a ramuscule to the genio-hyoideus, and finally terminates in a series of 

 branches analogous to those of the gustatory nerve, and which mix with 

 them. 



These branches are therefore refiected upwards, bending round the 

 posterior border of the hyo-glossus brevis, and pass into the interstice between 

 that muscle and the genio-glossus. They are distributed to all the muscles 

 of the tongue. 



The hypoglossals, being motor nerves, cause the contraction of the 

 muscles of the tongue during the movements proper to mastication and the 

 production of the voice. Though they most frequently act together, yet 

 they may do so separately, as in the unilateral movements of the tongue. 



DIFFERENTIAL CHARACTERS IN THE CRANIAL NEBVES OF OTHER THAN SOLIPED 



ANIMALS. 



In the domesticated mammals, the cranial nerves offer the greatest analogies ; their 

 origin U the same in all, and it is only in their distribution that we find some vaiiety, 

 due to the difference in the form of the head. Consequently, in this comparative analysis 

 we si) all not discover any fundamental differential characters. 



EuMiNANTS. — There is no difference to note in the four first pairs. 



Triqeminal nerve. — Divided into three branches as in Solipeds. It has been stated 

 that in Ruminants the ophthalmic branches are dibtributed to the majority of the muscles 

 of the eye ; iu the Sheep we have only seen the palpehro-nasal nerve offering Ihis relation- 

 ship to the motor organs of that part. The anterior palatine nerve is relatively 

 voluminous. . 



Facial nerve, — Towards the middle of its subparotideal course, this gives ott a large 

 anterior auricular nerve : when it arrives at the middle of the posterior border of the 

 masseter muscle, it divides into two branches. The inferior branch passes obliquely down- 

 wards and forwards, towards the mental foramen, where it terminates as in the Horse ; 

 it' furnishes an anastomotic branch to the superior. The latter crosses the middle 

 portion of the masseter, and becomes mixed with the suborbital ramu.-cules of the fifth pair ; 

 iibout the middle of its course it receives a filament from the superficial temporal nerve. 

 We need not allude to the auditory and glosso-pliaryngeal nerves, except to say that the 

 latter communicates with the pneumogastric soim after its exit from the foramen lacerum. 



Pneumoqastric nerve. — This offers numeious differences in its rc.ots and distribution. 



In the Ox and Sheep, the sensitive roots arise from an iiregukily elliptical suiface 

 comprising the whole of the respiratory tract. They are from fifteen to twenty in 



