lie produced by the exiinial Mufcles ? 309 



talUne, as aftei* couching or extradion. For thefe and other reafons his attention was 

 more particularly clireded to the external mufcles. 



Upon carefully removing the eyelids, the mufcles of the eye prcfent themfelves to view in 

 number fix ; four called redi or ftraight, and two oblique, fo named from their direction. 

 In Pkte XIII. Fig. 4, AAAA rcprefent the tendons of the refti mufcles, where th.ey are in- 

 ferted into the fclerotic coat, at the anterior part of the eye. B, the fuperior oblique, or 

 trochlearis, as fometimes called, from its pafiing through the loop or pulley connetled to 

 the lower angle of the orbit or notch in the os frontis ; it pafles under the fuperior reflus 

 jnufcle, and backwards to the poftcrior part of the eye, where it is inferted by a broad flat 

 tendon into the fclerotic coat. C, the inferior oblique, arifing tendinous from the edge of 

 the orbit or procefs of the fuperior maxillary bone, paffing flrong and flefhy over the in- 

 ferior reftus, and backwards under the abduifor to the poRerior part of the eye, where it 

 is alfo inferted by a broad flat tendon into the fclerotic coat. DDD, the fat in which the 

 eye is lodged. In Figure 5, the bones forming tiie external fide of the orbit, with a por- 

 tion of the fat, are removed, by which we have a dillinft view of the abduftor. ARC, three 

 of the refti mufcles, ariTing from the back part of the orbit, paffing ftrong, broad and flefhy 

 over the ball of the eye, and irrferted by flat broad tendons into the fclerotic coat, at its in- 

 terior part. D, the tendon of the fuperior oblique mufcle. E, the inferior oblique. In Fig. -6, 

 A reprefents the abductor of the eye. B^the flefhy belly of the fuperior oblique, arifing 

 ftrong, tendinous and fkfhy from tlie back part of the orbit. C, the optic nerve. D and E, 

 the re£li mufcles. 



The life afcribed to thefe difFerent mufcles is that of dlre£iing the axis of the eye towards 

 the difl^erent objefts, or to exprefs the paffions of the mind. But Dr. Hoflack rationally In- 

 fers, from the general application of the combined forces of mufcles through the whole of 

 ihe animal fyftem, that this fet of mufcles, which he conceives to be well adapted to produce 

 the focal adjullment, may alfo be employed on that objeiSb. He afiumes, as the neceflary 

 confequence of contraiflion in thefe mufcles, that the axis of the eye will be elongated, and 

 the elaftic cornea rendered more convex ; both which circumftances would tend to preferve 

 diftin6lnefs of vifion with regard to near objeifts. For as fuch objefts afford a focal image 

 more diftant from the refrafling furface, through which the light may pafs, the elongation 

 cf the axis will be of advantage, by removing the retina further back ; and the increafed 

 convexity and fhortencd focus of the cornea will conduce to the fame end. 



How far the aflion of the rcfti mufcles might produce an elongated figure, is perhaps 

 capable of difputc; though this efFcft will probably be admitted without hefitation, as a con- 

 fequence of the contia£lion of the oblique mufcles But to put the matter out of doubt, 

 whether this organ be capable of having its focal adjuflment confiderably varied by external 

 preflTurc, our author applied the common fpeculum oculi to his own eye. With a very 

 moderate prefTure, while directing his attention tfi an obje£l at the dillance of about twenty 

 yards, he faw it diftinflly, as alfo the difl^crent itit rmediate objefis; but endeavouring to 

 look beyond it, every thing appeared confufed: h u increafed the preflure conGderrihlyt in 

 confequence of which he was enabled to fee object mltinftly, though placed mucKnear^r t'lan 

 the natural focal diltance For example : he held 'iforc his eye, at the diflinto of about rwo . 

 inches, a printed book. In the natural ftate of tlie eye, he could neither diflinguifh the linss 



