LACIIYMAL ORGANS. 



99 



of the palatine branch of the upper jaw. 

 Cloquet* calls this pouch intermaxillary sinus 

 or sac. In venomous serpents, the lacrymal 

 canal opens, as in the mammifera, in the ex- 

 ternal wall of the nasal fossae. 



There is no lacrymal apparatus in fishes. 



In the description of the lacrymal gland in 

 man, the intimate structure of it in the lower 

 animals has been already alluded to. The re- 

 mark of Miiller may be repeated here, that 

 similar glands have often a perfectly different 

 structure in different animals; of which the 

 lacrymal gland examined in the chelonia, birds, 

 and mammifera affords an example. 



The lacrymal bone contributes to separate the 

 orbit from the cavity of the nose. It is wanting 

 in certain mammifera, as the phocae and most 

 cetacea. It is enormously developed, on the 

 contrary, in certain others, as the giraffe, stag, 

 &c. It exists also in birds, and forms in them 

 often the greatest part of the inferior margin of 

 the orbit. In reptiles, its existence is variable. 

 It is found in crocodiles. It is absent in the 

 chelonia, ophidia, and batrachia. It is also 

 wanting in fishes, unless the first infra-orbital 

 be assumed as analogous to it. 



In ruminating animals, remarkably so in deers 

 and antelopes, the infra-orbital fossa of the su- 

 perior maxillary bone is very large, and is lined 

 by a reflection of the skin, more or less in the 

 form of a sac. The skin, which has assumed 

 the characters of a mucous membrane, contains 

 in its substance numerous follicles,which secrete 

 a thick blackish unctuous humour a secretion 

 which appears to have some relation with the 

 sexual function. This matter has been impro- 

 perly called tears, hence the French name 

 larmiers of the infra-orbital glandular sacs of 

 ruminants. In the sheep these organs are re- 

 presented by a mere fissure extending on the 

 side of the nose from the nasal canthus. 

 Meckel compares to this structure the foveae 

 in the face, behind the nostrils, of several poi- 

 sonous serpents, such as the rattle-snake ; but 

 the membrane lining these parts scarcely ap- 

 pears to secrete anything. The temporal gland 

 of the elephant seems to be of the same nature 

 as the infra-orbital glandular sacs of rumi- 

 nants. 



Development of the accessory parts of the 

 eye.f The accessory parts of the eye appear 

 subsequently to the eyeball, and, as is the case 

 with the accessory parts of the organ of hearing 

 in reference to the labyrinth or ear-bulb, have 

 quite a separate and distinct origin from it. 

 That the development of the accessory parts of 

 the eye is independent of that of the eyeball is 

 confirmed by the anomalous conformation which 

 the organ has been sometimes found to present; 

 thus Malacarne relates a case in which the eye- 

 balls, their nerves and muscles were wanting, 

 whilst the lacrymal apparatus and eyelids were 

 regularly developed. 



Up to the eighth week the external integu- 



* Op. cit. 



t Burdach, Die Physiologic, als Erfahrungs- 

 wisscnschaft; &c. and Valentin, Entwickelungs- 

 gcschichtc. 



ment passes quite smoothly over the eyeball. 

 The conjunctiva is then partitioned off by the 

 formation of a linear fold, which, in the ninth 

 week, surrounds the anterior surface of the 

 eyeball like a small ring. The upper and lower 

 parts of the fold progressively enlarge until 

 they meet each other over the eyeball, which 

 takes place about the twelfth week. 



The progress of the development of the eye- 

 lids is sometimes arrested, so that mere folds of 

 skin have been found occupying their places, or, 

 development having proceeded a little further, 

 the eyelids have been found presenting their 

 regular conformation indeed, but too short to 

 cover the eyeball and incapable of motion. 



Having met, the edges of the eyelids ad- 

 here by the extension of the epidermis from 

 the one to the other. In the human embryo 

 the adhesion between the eyelids by the exten- 

 sion of the skin ceases towards the latter 

 months, but the edges continue sticking together 

 by the Meibomian secretion until the period of 

 birth. In the young of several of the mammi- 

 fera, as the carnivora and rodents, the eyelids 

 continue closed for some time after birth 

 from one to two weeks. In birds, even in the 

 embryo state, the eyelids never unite. 



Sometimes adhesion between the eyelids in 

 the human subject is found at birth, constitut- 

 ing what is called congenital anchyloblepharon ; 

 and this may be either immediate or by the 

 intervention of a membranous structure. 



The closure of the pupil by the pupillary 

 membrane in the fetus corresponds to the ad- 

 hesion of the eyelids to each other at that period. 

 According to Meckel the pupillary membrane 

 continues entire in animals born blind, as it is 

 expressed, as long as the eyelids remain closed. 



The tarsal cartilages first appear distinctly in 

 the fifth month ; and at birth, that of the up- 

 per is perfectly developed. The eyelashes first 

 appear free about the sixth month. 



The lacrymal gland is already evident in the 

 last half of the fourth month. 



The inner canthus of the eye is at first more 

 elongated than it is afterwards. 



On the first appearance of the eyelids, 

 Burdach tells us, the lacrymal caruncle presents 

 itself; and at the inner angle a diverticulum of 

 the conjunctiva sinks down to the oro-nasal 

 cavity as the commencement of the lacrymal 

 sac and nasal duct. The lacrymal points 

 project very much in the fifth month, and in 

 the seventh are somewhat more retracted. The 

 lacrymal apparatus in general, as also the 

 Meibomian follicles, are proportionably much 

 developed at an early period. 



BIBLIOGRAPHY. See that of article EYE and 

 the several works referred to in the course of 

 this. The most complete, indeed, so far as I 

 know, the only inonography, is that of John Chris- 

 tian Rosenmuller, " Partium externarum oculi hu- 

 niani imprimis organorum lacrymalium descriptio 

 anatomica, iconibus illustrata." Lipsiae, 1810. In 

 this will be found a catalogue raisonne of all pre- 

 ceding works bearing on the subject. 



( T. Wharton Jones.) 

 H 2 



