94 



LACRYMAL ORGANS. 



ment, produced partly by the vessels crossing 

 over each other simply, and partly by inoscu- 

 lations. The latter is particularly the case 

 around the cornea. It is only in the inflamed 

 state in catarrhal ophthalmia that the vessels 

 of the ocular conjunctiva can be well seen. 

 In catarrhal ophthalmia, large superficial tor- 

 tuous vessels are observed proceeding in a di- 

 rection towards the cornea ; a few of the same 

 size are seen crossing these, especially at a dis- 

 tance from the cornea. Underneath the large 

 vessels is a network of smaller ones, the 

 branches of the larger. The arrangement of 

 the vessels around the margin of the cornea 

 has been already noticed. It can scarcely be 

 doubted that the large dark-coloured varicose 

 vessels, derived from the muscular, seen in the 

 conjunctiva in the so-called arthritic states of 

 the eye, are veins, as also the largest and most 

 tortuous of those seen in catarrhal ophthalmia. 

 Of the two sets of vessels distributed to the 

 conjunctiva, one set supplies the conjunctiva 

 forming the palpebral sinuses, the other that 

 part of the conjunctiva which corresponds to 

 the tarsal cartilages. Both sets give off nu- 

 merous branches, which subdivide very mi- 

 nutely in the papillary body. The second set, 

 after having given off their ramifications to the 

 papillae, proceed towards the margins of the 

 eyelids ; following, in the upper, a straighter 

 and more parallel direction than in the lower. 



2. Veins. The veins from the eyelids dis- 

 charge their blood into the anterior and pos- 

 terior facial veins. 



The blood from the other accessory parts of 

 the eye is returned to the cavernous sinus by 

 the ophthalmic veins, of which there are two 

 to each eye : one called the cerebral oph- 

 thalmic, and the other the facial ophthalmic 

 vein. 



Cerebral ophthalmic vein. Larger than the 

 facial ophthalmic vein, this begins at the inner 

 angle of the eye, from the upper end of the an- 

 terior facial vein. From this it passes back- 

 wards through the orbit to the inner part of the 

 superior orbital fissure, by which it enters the 

 cranium, where it empties itself into the caver- 

 nous sinus seldom into the circular sinus. 

 In this course it has several communications 

 with the facial ophthalmic. The cerebral oph- 

 thalmic vein receives directly or indirectly, 

 besides the veins from the different parts of the 

 eyeball and its muscles, a vein from the lacry- 

 mal sac, and from the parts lying at the inner 

 canthus ; the anterior nasal vein, the lacrymal 

 vein, and the posterior nasal vein. 



Facial ophthalmic vein. This receives the 

 infra-orbital and some other deep veins of 

 the face, besides some veins from the eyeball. 

 The deep branch of the anterior facial vein 

 takes one of its origins from it. The facial 

 ophthalmic vein leaves the orbit by the supe- 

 rior orbital fissure, and opens into the cavernous 

 sinus below the cerebral ophthalmic. 



Comparative anatomy and development. 

 In the description just given of the accessory 

 parts of the human eye, allusion has been occa- 

 sionally made to their structure in the lower 

 animals ; here such further observations will be 



offered as may tend to illustrate their physiolo- 

 gical importance in the animal series. 



And first, it may perhaps be well to keep in 

 mind that, although generally speaking, organs, 

 traced from the higher to the lower animals, are 

 observed to become depreciated in develop- 

 ment; still that this is by no means always 

 the case in a ratio corresponding to the posi- 

 tion of the animal in our classifications. For 

 the circumstances connected with the mode of 

 life of an animal, be it mammal, bird, reptile, 

 or fish, may be such as to call for a greater or 

 less development of some particular organ. 

 Thus, though in the mammifera we find the 

 eyelids very perfectly developed, and in fishes 

 in an extremely imperfect state, or entirely 

 wanting, and though we find gradations be- 

 tween these two extremes in the animals hold- 

 ing an intermediate place, still there exist 

 mammiferous animals in which the integument 

 passes right over the eyeball without forming 

 any palpebral fold ; and there are fishes in 

 which there are not only palpebral folds, but 

 also an orbicular muscle. Again, the semi- 

 lunar fold of man and the higher quadrumana 

 is enlarged in quadrupeds into the membrana 

 nictitans, and in birds forms the very artificially 

 constructed third eyelid, which subsists, though 

 in a less perfect state, in reptiles, but in fishes, 

 where the structure does exist, it is found again 

 reduced to asemilunar fold. In man the lacry- 

 mal gland is large. In the lower mammifera 

 generally, in birds, and in the higher reptiles the 

 lacrymal gland is also found. But it is small 

 in proportion to another gland situated at the 

 nasal canthus of the eye, the glandule of 

 Harder, which is developed in a direct propor- 

 tion with the membrana nictitans, or third eye- 

 lid, and to which it therefore belongs. In man 

 and the quadrumana there is no trace of the 

 glandule of Harder. It is incorrect to view the 

 lacrymal caruncle in that light, for both may- 

 exist together. 



Besides these differences in the development 

 of the accessory parts of the organ of vision 

 observed in the animal series and capable of 

 being generalised, there exist specific and indi- 

 vidual differences which can only be noticed in 

 detail. 



1. Eyelids. 



In subterranean mammifera, as the blind rat, 

 the chrysochloris of the Cape, the common 

 mole ; among reptiles, in the pipa, which lives 

 in obscure places ; and in perennibranchiate 

 batrachia, which inhabit subterranean lakes 

 or marshes, as the proteus and syren ; and in 

 fishes which burrow in the mud or sand, as 

 the anguilliform and certain cyclostomatous 

 fishes, the eyes are very small, and the common 

 integument passes right over them without 

 forming any palpebral fold. In the Ophidian 

 reptiles as first pointed out by Jules Cloquet ; 

 in Geckoes among the Saurian reptiles, as 

 shewn by J. Mu'ller; and even in the blind rat, 

 according to the latter author, there is a com- 

 pounding of the simple continuation of the in- 

 teguments over the eyeball, as described above, 

 with the existence of a conjunctiva underneath, 

 enclosing an oculo-palpebral space. This struc- 



