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Show 1870.] OESOPHAGUS OF SAUROPSIDA. 285 fibre was not found to compose the sheath of the oesophagus of either Birds or Reptiles, while a coat of this fibre was always seen to invest more or less of the oesophagus of Mammalia and Fishes. Here, then, is a remarkable character in which Birds and Reptiles agree together and differ from Mammals and Fishes. Nor is it less noteworthy that while Sauropsida are thus distinguished by the absence of striated muscular fibre on the oesophagus, they are, on the other hand, equally distinguished by the presence of this fibre within the eye. At least I have never found striated muscular fibres in the eye of any mammal or fish, nor have I ever failed to find those fibres in the eyes of Sauropsida; and this agrees with the older observations of other anatomists. But further researches are yet required on this subject. So, too, of the oesophageal sheath, both in the larval and perfect states, of Batrachia. As of Lepidosiren, a reputed fish, the blood-disks, according to m y observations (Ann. Nat. Hist. October 1848, and Proc. Zool. Soc. 1862, fig. 17, p. 101), have a Batrachian character, it would be interesting and instructive to compare the oesophageal sheath of this creature with the same part of other allied vertebrates. In m y note-book occurs the following account: - " D e c . 14, 1848. Lepidosiren from the West Coast of Africa: oesophagus membranous, wide and very dilatable, many striated muscular fibres mixed with smooth ones on the gullet backwards, as far as the hind end of the pericardium; the oesophagus a third of an inch further back, and thence to the stomach, quite destitute of any thing like striated muscular fibre." This examination is at present worthless, from a want of the comparisons above mentioned, but may prove valuable whenever they are made. As already noticed, I have never found the whole oesophagus of Fishes and Mammalia destitute of a sheath of striated muscular fibre; and in certain sections of the class Mammalia the extent of that sheath is so different as to afford, so far as my observations have gone, good diagnostics. Thus in the Rodentia and Ruminantia this striated fibre does, and in M an and Quadrumana does not, invest the cardiac end of the oesophagus. And in different sections of one and the same order there may be similar differences; of the Carnivora, e.g., the striated muscular fibre does not clothe the cardiac extremity of the nesophagus in the Felidae, but extends quite to that termination in the Ursidse. That such differences are always invariable cannot, in the present state of our knowledge, be peremptorily affirmed; but that they are constant in many vertebrates is certain. How far such characters may tend to favour the validity of the great group of Sauropsida, or of only the two primary vertebrate sections of Pyrenaemata and Apyrenaemata (Proc. Zool. Soc. 1862, p. 91, and Journ. Anat. and Phvs. v. 2), remains to be seen by the light of more knowledge. Finally, when all the diagnostics between Sauropsida and M a m malia are well and truly reviewed, it now appears that the characters furnished by the intimate structure of the muscular fibre must receive more attention than has hitherto been given to them. PROC. ZOOL. Soc-1870, No. XX. |
