250 SENSE OF SIGHT. 



lumn as other respiratory nerves. The coincidence of this twinkling, 

 and of the motion of the eyeball upwards, was, therefore, easily under- 

 stood. 



There is a difficulty, however, here, which has doubtless already sug- 

 gested itself to the reader. The fourth pair is distributed to the supe- 

 rior oblique only; the lesser oblique receives none of its ramifications. 

 They cannot, therefore, be identically situate in this respect. Yet 

 they are both considered by Sir Charles Bell as involuntary muscles. 

 The action, indeed, of the lesser oblique would appear to be even more 

 important than that of the greater oblique, as the function of the 

 former, when acting singly, is to carry the eye upwards and inwards ; 

 and, when the action of its antagonist is abolished, this is more clearly 

 manifested. Sir Charles found, that the effect of dividing the supe- 

 rior oblique was to cause the eye to roll more forcibly upwards ; in 

 other words, it was given up, uncontrolled, to the action of the anta- 

 gonist muscle. This difficulty, although it is not openly stated by Sir 

 Charles, must have impressed him ; for, after having referred to the 

 effect of the division of the superior oblique, he is constrained to 

 suggest an influence to the fourth pair, which would, we think, be 

 anomalous: that it may, on certain occasions, cause a relaxation of 

 the muscle to which it goes, and, in such case, the eyeball must be 

 rolled upwards! In addition to this, too, as Mr. Mayo 1 has observed, 

 the distribution of the muscular nerves of the eye is not such as 

 to allow of our opposing the straight muscles to the oblique; and one 

 cogent reason is, that the third pair supplies part of each class. 



We have still, therefore, much to learn regarding this subject, into 

 which so much interest, and, at the same time, so much uncertainty 

 has been infused. In some experiments on the fresh subject, made by 

 the author with Professor Pancoast, who carefully separated the differ- 

 ent muscles, with the view of discovering their precise action, it was 

 clearly apparent, that the oblique muscles act in the manner above 

 mentioned; the superior oblique directing the eye slightly inwards and 

 downwards; and the inferior, rolling it upwards and inwards, when 

 they acted singly : when the two were brought into action, simultane- 

 ously, they appeared to antagonize each other as rotators, but pro- 

 jected the eye forward. It would seem, indeed, that an important use 

 of these muscles is to keep the eye prominent during the action of the 

 straight muscles. 



These results harmonize greatly with the deductions from experi- 

 ments on living animals by Mr. Bransby Cooper. 2 He divided the 

 superior and inferior oblique muscles on the eyes of several living 

 rabbits; and inferred, that the oblique muscles, when acting together, 

 suspend the eyeball in a central position in the orbitar cavity ; moderate 

 the retracting influence of the four straight muscles; and, when acting 

 in succession, without being restricted by the influence of the straight 

 muscles, they roll the eye on its own axis, drawing the globe forward, 

 and at the same time tending, in a great degree, to extend the sphere 

 of vision. 



1 Outlines of Human Physiology, 4th edit., p. 299, London, 1837. 

 9 Guy's Hospital Reports, vol. iii., April and October, 1838. 



