OCR Text |
Show 1894.] TELEOSTEAN MORPHOLOGY. 427 are the solid walls of the skull; below is the interorbital septum ; above, the firm dorsal muscles and anterior interneural spines. O n the left or inner side are the coalesced limbs of the left ectethmoid and sphenotic, separated from the parasphenoid by the foramen already mentioned. Thus expansion is only possible on the right or outer side, occupied by the eye, and on such part of the left or inner side as is pierced by the foramen. The organ is rather richly supplied with blood by a branch coming from the vessel corresponding to the external carotid artery of higher animals. This branch passes to the inner face of the organ, whether left or right, and breaks up into numerous smaller vessels on that surface. I have already mentioned the large pad of adipose tissue which underlies and more or less surrounds the left organ in the Halibut. It consists optically of a mass of connective tissue very closely beset with minute oleaginous globules. The whole is more or less elastic, and must add considerably to the contractility of the organ it surrounds. To a less extent adipose matter is found in the neighbourhood of the organ of the blind side in most species which I have examined. I have studied the internal structure of the organ in various species in the ordinary way, by means of microscopic sections, but can find no trace of any glandular structure. The walls of the organ and the interlacing muscular bands are merely lined with ordinary flat epithelium cells. The liquid noticed as occurring both in the organ and in the general orbital cavity is coagulated, by the action of reagents, into a finely granular plasma, taking on a faint pink stain in borax-carmine. It is indistinguishable optically from the substance met with in similar preparations of some of the brain-cavities of young fish. Professor Howes has drawn m y attention to the fact that a similar fluid is met with in mesenteric and synovial cavities, and, in the absence of any definite secretory apparatus, is assumed to be deposited there by the blood-vessels through the medium of the ordinary epithelium cells. It seems permissible to draw the same inference in the case of the organ now under discussion, and to consider that the richness of the blood-supply is associated with the production of the fluid. Similar fluid is present in the orbital cavities of fish in which the recessus is not developed, but of course m a less quantity. Function. We have seen that the cavity of tbe orbit and of the recessus orbitalis is filled during life with a fluid which has, without doubt, the function of supporting the orbit, since the sinking of the eyes which is always, unless averted by artificial means, to be observed in stale fish, seems to be chiefly due to the coagulation and consequent shrinkage of the fluid contents of the orbital cavities. It will be familiar to most observers that, whereas in a " round |