The palpebral and oculomotor apparatus in fishes : observations on morphology and development / by N. Bishop Harman.

  • Harman, Nathaniel Bishop, 1869-1945.
Date:
[1899]
Catalogue details

Licence: Public Domain Mark

Credit: The palpebral and oculomotor apparatus in fishes : observations on morphology and development / by N. Bishop Harman. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    19/52 (page 19)
    The close relation which spiracle and eyelids have in the- •embryo and young fish is not apparent from examination of adult species; in the latter, growth has separated the two con- siderably. A compiirison of the measurements of the shortest distance between the palpebral fissure and the spiracle to the length of the palpebral fissure will illustrate this. The propor- tion is shown in an index giving the ratio of palpebral-spiracle distance to the palpebral fissure length taken as 100 :— Fish. Lenj^th of Fish. Palp. Fissure. Palp. Fiss. to Spiracle. Index of ! Approximation. Galeus (adult) about 1000 mm. 85 mm. 25 mm. 71 Mustelus (do.) ,, 700 ,, 25 „ 10 ,, 40 i ,, (embryo) 260 ., 12 ,, 1-5 ,, I.-i ! „ (do.) „ 200 ,, 8 1 12 >. (do.) „ 70 „ 5 ,, 0-5 „ 10 Regarding the ultimate source of origin of the muscle masses above described, the relation which the ordinary branchial muscle anlages are found to bear to the dermis is the same as that generally accepted. This dermal tissue has been shown to be the derivative of the outer layer of the myotome, so their source is that common to all muscle tissue, but the indirectness of their connection indicates an evolution antecedent to such muscle tissue as that of the limb-buds where the derivation is a direct one. Of the presence of the most superficial mass of muscle tissue arising within the superficial dermis in the higher branchial segments (figs. 11 and 12, m.s.s.), I can find no record of previous observations. In time of origin it is later than the other branchial musculature, but its dermal source, since it is the more superficial, indicates an origin from an earlier dermal outgrowth from the myotome, but whether this will show the morphological value of the muscle as of primitive or later evolution I am unable to determine. The conclusion of these ohservations is that the muscnlaiure of the eyelids of Mnstelus is derived from a musenlature inimarily belonging to the sinracle ; also that there is evidniee to shov that