Surgical anatomy : a treatise on human anatomy in its application to the practice of medicine and surgery . leus in the fioor of the aqueduct of Sylvius. It is a motor nerve, andsupplies all the muscles of the eyeball except the superior oblique, the externalrectus, and radiating fillers of the iris. The Fourth Cranial, Pathetic, or Trochlear Nerve is the smallest of thecranial nerves, and apparentlj^ arises at the outer side of the crus cerebri. Itsreal superficial origin is from the valve of Vieussens, or superior medullary velum,immediately behind the testes or posterior pair of corpora c[u
Surgical anatomy : a treatise on human anatomy in its application to the practice of medicine and surgery . leus in the fioor of the aqueduct of Sylvius. It is a motor nerve, andsupplies all the muscles of the eyeball except the superior oblique, the externalrectus, and radiating fillers of the iris. The Fourth Cranial, Pathetic, or Trochlear Nerve is the smallest of thecranial nerves, and apparentlj^ arises at the outer side of the crus cerebri. Itsreal superficial origin is from the valve of Vieussens, or superior medullary velum,immediately behind the testes or posterior pair of corpora c[uadrigemina. Thedeep origin is from a nucleus in the floor of the aqueduct of Sjdvius in close rela-tion with the nucleus of the oculo-motor nerve. In the substance of the valve ofVieussens it decussates with the oi^posite fourth cranial nerve. It then windsaround the outer side of the crus cerebri, and appears at the base of the brain atthe anterior border of the pons. , It is a motor nerve, and supplies the superioroblique or trochlearis muscle. PLATE CCLXV. External geniculatebody Internal geniculate. Affected portion ofretinae of both eyes Affected optic tract IIAGRAM OF OPTIC TRACTS,463 THE CRANIAL NERVES. 465 The Fifth Cranial, Trigeminus, or Trifacial Nerve, the largest of the cranialnerves, arises from the sides of the pons by two roots—a larger, posterior or sen-sory root, and a smaller, anterior or motor root. These roots can be traced to thefloor of the fourth ventricle and to the gray matter in the lower part of themedulla oblongata and in the upper part of the spinal cord. It is the only cranialnerve which resembles a spinal nerve in arising by two roots,—a posterior, orsensory, and an anterior, or motor,—and in having a ganglion on the poste-rior root. The trifacial is a mixed nerve. It distributes sensory filaments tothe dura mater, pia mater, oibit, eyelids, nose, gums, teeth, tonsils, palate, sphenoidcells, ethmoid cells, frontal sinus, maxillary sinus, na
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