54 
THOMPSON YATES LABORATORIES REPORT 
Sensory Disturbances produced by Section of the Vth Cranial, as observed 
IN THE Monkey 
Skin. 
The whole of the side of the face in front of the anterior border of the sensory skin-field 
of the Ilnd cervical nerve [vide infra, under Ilnd cervical nerve, p. 66, and fig. 6, p. 67), is 
completely insensitive. Along the median line, the cross lap of the skin-field of the Vth cranial 
of tlie opposite side is everywhere slight, it is greatest on the scalp, amounting to, perhaps, 5 
millims. ; on the lip it is barely demonstrable. 
When the animal drinks, which it does without apparent hesitation or difficulty, it begins 
by placing its muzzle fairly in the centre of the basin, but it then almost directly proceeds, while 
drinking, to shift its head sidewise in a direction away from the side of the nerve-section. This 
deviation of the head is only limited by the muzzle finally meeting the edge of the dish in the 
direction of the uninjured side, and against that it is kept, the draught continuing to be taken from 
the corner of the dish on that side. If the dish be shifted, when the animal starts drinking from 
it again he starts from the middle of the dish as before, and then gradually shifts over as before and 
to the same corner. The phenomenon seems attributable to the recognition of the food by sensory 
impressions arising from the muzzle, and from one side of it only, the eyes being too near to the 
pan to be used while the drauglit is being taken. The animal keeps turning its neck in the 
direction of the one side upon which the food is actually felt, believing the food to lie chiefly in 
that direction. Space-perception here, therefore, depends much on trigeminus. 
The Tongue. 
Sensation is completely abolished on the dorsum of the tongue, from the tip backwards, to 
just in front of the circumvallate papillae. When the trigeminus of one side only is severed, the 
area whence no response to touching, or pinching, or heat can be elicited, has the limits 
represented in fig. i. It will be noticed that the posterior border is a sloping one, running parallel 
with, and about 2 millims. in front of the row of circumvallate papillae. It will be also noticed 
that the field extends apparently fully up to the median line, — in other words, an overlap of the 
fields of the right and left trigeminal nerves (crossed overlap) across the median line of the dorsum 
of the tongue is very slight or non-existent. 
The frenum and the side of the tongue, except beliind the level of the line of circumvallate 
papillae, give no response to mechanical or thermal excitation. 
The Gums and Inside of the Cheek. 
The gums on the side of the section give no response to mechanical or thermal excitation, 
neither does the mucous membrane lining the cheek, which is in the Monkey peculiarly sensitive. 
The Palate. 
The half of the hard palate corresponding with the side of the nerve-section gives 
no response to mechanical or thermal excitation. So also the half of the soft palate and of the 
