NERVUS ABDUCENS. 599 



Landois found that in the famous case of Romberg, a man named Schwann, the sphygmo- 

 graphic tracing of the carotid pulse of the atrophied side was distinctly smaller than on the 

 sound side. 



Urbantschitsch made the remarkable observation that stimulation of the branches of the 

 trigeminus, especially those going to the ear, caused an increase of the sensation of light in the 

 person so stimulated. Blowing upon the cheeks or nasal mucous membrane, electrical stimula- 

 tion, the use of snuff, smelling strong perfumes all temporarily increase the sensation of light. 

 The senses of taste and smell, as well as the sensibility of certain areas of the skin, can all be 

 exalted reflexly by gentle stimulation of the trigeminus. In intense affections of the ear, whereby 

 the fibres of the trigeminus are often affected sympathetically, these sensory functions may be 

 diminished. As the ear-malady begins to improve, the excitability of these sense organs also 

 again begins to improve. 



[Complete section of the trigeminus results in loss of sensibility in all the parts 

 supplied by it (fig. 430), including one side of the face, temple, part of the ear, the 

 fore part of the head, conjunctiva, cornea, mouth, gums, Schneiderian mucous 

 membrane, anterior two-thirds of the tongue, and part of pharynx. In drinking 

 from a vessel, the patient feels as if one side of it were cut away. The muscles of 

 mastication are paralysed on that side, food is not chewed on one side, and fur 

 accumulates on the tongue on that side. The mucous membranes tend to ulcerate, 

 that of the mouth being chafed by the teeth, the gums get spongy, the nasal 

 mucous membrane tends to ulcerate, so that smelling is interfered with, and 

 ammonia excites no reflex acts, while the eye undergoes panophthalmia.] 



[Gowers is of opinion that the sensation of taste on the posterior part of the tongue, soft 

 palate, and palatine arch depends on the fifth nerve and not on the glossopharyngeal nerve.] 



348. VI. NERVUS ABDUCENS. Anatomical. It arises slightly in front of and partly 

 from the nucleus of the facial nerve (which corresponds to the anterior horn of the spinal cord), 

 from large-celled ganglia in the deeper part of the anterior region of the fourth ventricle, 

 (emenentia teres, fig. 427). [Its nucleus is connected with the nucleus of the third nerve of 

 the opposite side. It appears at the posterior margin of the pons (fig. 428, VI. ). This nerve 

 has a very long course before it enters the orbit, and as it bends over the posterior margin of 

 the pons, it is liable to be compressed there or from pressure upon the tentorium cerebelli, so 

 that both nerves are very liable to paralysis.] 



Function. It is the voluntary nerve of the external rectus muscle. In co- 

 ordinated movements of the eyeballs, however, it is involuntary. 



Anastomoses. Branches reach it from the sympathetic upon the cavernous sinus (fig. 429). 

 A few come from the trigeminus, and their function is analogous to similar fibres supplied to 

 the trochlearis and oculomotorius. 



Pathological. Complete paralysis causes squinting inwards [or convergent squint] and con- 

 sequent diplopia. [The eye cannot be rotated outwards beyond the middle line, the double 

 images are in the same horizontal plane and vertical, the false one is to the left of the patient's 

 eye when the left eye is affected (fig. 426, 2). The feeling of giddiness is often severe. There 

 is secondary deviation to the inner side, and the head is turned towards the affected side.] In 

 dogs, section of the cervical sympathetic causes a slight deviation of the eyeball inwards (Petit). 

 This is explained by the fact that the abducens receives a few motor fibres from the cervical 

 sympathetic. Spasm of the abducens causes external squint. 



Squint. In addition to paralysis or stimulation of certain nerves producing squint, it is to 

 be remembered that it may also be caused by a primary affection of the muscles themselves, 

 e.g., congenital shortness, contracture, or injuries of these muscles. It may also be brought 

 about owing to opacities of the transparent media of the eye ; a person with, say an opacity 

 of the cornea, rotates the affected eye involuntarily, so that the rays of light may enter the eye 

 through a clear part of the media. 



349. VII. NERVUS FACIALIS. Anatomical. This nerve consists entirely of efferent fibres, 

 and arises from the floor of the fourth ventricle from the "facial nucleus" (fig. 427, 7), which 

 lies behind the origin of the abducens, and also by some fibres from the nucleus of the abducens 

 [although Gowers' observations do not confirm this ( -366)]. Other fibres arise from the 

 cerebrum of the opposite side ( 378, I. ). It consists of two roots, the smaller portio inter- 

 media of Wrisberg forms a connection with the auditory nerve (see 350). The original 

 fibres of the portio intermedia are developed from the glossopharyngeal nucleus (Sapolini). It 

 would thus appear that the sensory and gustatory fibres which are present in the chorda tympani 

 enter it through these fibres (Duval, Schultze, Vulpian), so that the portio intermedia is a special 

 part of the nerve of taste, which becomes conjoined with the facial, and runs to the tongue in 

 the chorda. Along with the auditory nerve, it traverses the porus acusticus interims, where it 



