1910.] A fferents of Third, Fourth, and Sixth Cranial Nerves. 453 



sources of the afferent nerve-fibres of the several extrinsic ocular muscles we 

 have had recourse to the degeneration method. Our experiments of this 

 kind fall under six lieadings. 



I. Severance of the Third Cranial Nerve at its Origin frovi the Peduncle of 

 the Ccrehrnm. — Eleven experiments, including five with Dr. E. E. Laslett ; 

 one rabbit, three cats, seven monkeys. The time allowed for degeneration 

 has varied between 5 days at shortest and 5G days at longest. During life 

 the symptoms were the ptosis, external strabismus, and the dilatation of the 

 pupil well known to result from paralysis of the third nerve. 



Degeneration Besiifts. (I) Orhifal Nerves. — The nerve-trunks proceeding to 

 and entering the superior, inferior, and internal recti muscles and the inferior 

 oblique exhibited complete degeneration except for the fact that certain 

 minute myelinate fibres sparse in nuiiiber were quite sound. These fibres 

 vary in diameter between 2 ytt and 7 fi. Their number never exceeded 25 in 

 any one of the above muscle nerves : commonly there were from 6 to 12 of 

 them for each muscle ; in some cases, in some of the muscle nerves, none 

 at all were discoverable. The fibres resemble in size and appearance those 

 of the short ciliary nerves proceeding from the ciliary ganglion. The fourth 

 and sixth nerves, the branches of the ophthalmic division of the fifth nerve, 

 and the short ciliary nerves were entirely free from degeneration. 



(2) Orbited muscles. — In the superior, inferior, and internal recti muscles 

 and in the inferior oblique no intramuscular nerve-endings either of motor 

 or receptive (sensorial) type were found. At the tendon ends of these 

 muscles, in most cases, though not in all, there persisted a few undegenerate 

 nerve-fibres varying in diameter from 2 /x to 5 ; the greatest number found 

 in any one muscle was 13 (in inferior oblique). In two instances there were 

 found Golgi tendon-organs, one to three in number. In the control muscles 

 from the same orbit, namely external rectus and superior oblique, as also in 

 the muscles of the orbit of the opposite side, the usual abundance of 

 receptive nerve-endings as well as motor plates were visible, and the usual 

 abundance of tendon nerves. 



IT. Tntracrctnicd Severance of First Division of Fifth Nerve Just Distal to 

 Gasserian Ganglion. — One experiment (monkey). The period allowed for 

 degeneration was 15 days. The symptoms observable were anaesthesia of the 

 cornea, upper eyelid, and forehead. The pupil of the operated side was the 

 smaller. 



Degeneration Eesvlts. (1) Orbited Nerves. — In the frontal and nasal 

 branches (the lachrymal was not examined) of the fifth nerve no sound nerve- 

 fibres remained. In the branch from third nerve to internal rectus muscle 

 all nerve-fibres were sound : but the branch from third to inferior oblique 

 VOL. LXXXII. — B. 2 N 



