456 CONJUNCTIVA AND SCLEROTIC. 



course. It is, however, chiefly the trunk entering at the inner 

 commissure that contains the principal portion of the fibres, 

 and is hence remarkable for its size and the much larger num- 

 ber of its branches. He was able to establish this type of 

 aerve division in all the' specimens prepared from various 

 animals that he examined ; the less important differences met 

 with in a few instances, as, for example, a more or less superior 

 point of entrance of the internally situated main trunk, are only 

 incidentally mentioned. In consequence of the speedy division 

 and subdivision of the two principal trunks, and especially of 

 the inner one, a close and delicate plexus is formed, in which an 

 exchange of a few fibres takes place bet ween the smaller branches. 

 The principal portion of the branches constituting this plexus 

 stretches toward the anterior half of the conjunctival sac ; and 

 to its palpebral portion, whilst the fornix contains but few 

 small branches, and the visceral lamina of the same receives 

 generally only a third or fourth part of the nerves passing to 

 it. As has been already remarked, the number of the nerves 

 entering at the inner commissure of the conjunctival sac is far 

 greater than at the outer side, and this preponderance con- 

 tinues to be so expressed (notwithstanding the large number 

 of fibres given off for the supply of the membrana nictitans), 

 in the further distribution of the nerves, so that the branches 

 coming from the inner side pass beyond the antero-posterior 

 median line of the conjunctival expansion, and thus only the 

 smaller lateral portion of the sac is supplied with fibres coming 

 from the outer commissure. Moreover, so far as regards another 

 relation, namely, the proportion of nerves distributed to the 

 upper and lower lids, some variations occur, in accordance with 

 the special anatomical relations of the particular animal under 

 examination. In the Frog, for example, where the membrana 

 nictitans, by virtue of its peculiar arrangement and its large 

 extent, not only represents the lower lid, but also fulfils the 

 greater part of the functions which in other animals are per- 

 formed by the upper lid, the richness of its supply of nerves 

 may considerably exceed that of the latter. A modification 

 again occurs in Birds, where the membrana nictitans is indeed 

 present as an integral constituent of the conjunctival sac, but 

 in which the lower lid surpasses the upper in anatomical extent 



