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Show 284 MR. G. GULLIVER ON T H E [May 12, ments of which neither the significance nor the importance is very obvious. Besides, in the current ** Anatomy of Vertebrates,' the descriptions in this department are either so perfunctory or dogmatically incorrect as to repel research. Thus we have no notice whatever of the kind of muscular fibre composing the oesophageal sheath of any vertebrates, except when, in a comparison of this sheath of certain birds with that of ruminant mammalia (ii. p. 158, iii. p. 470), there occurs the singular notice that in this order the muscular fibres of the oesophageal coat "are of the striated kind." Hence the false doctrine might arise that the intimate structure of this muscular sheath is generally insignificant throughout the vertebrate subking-dom, and that the sheath of striated muscular fibre of the oesophagus in Mammalia is confined particularly to the order Ruminantia; whereas the oesophageal sheath of striped muscle is by no means confined in Mammalia to the Ruminants; for it exists more or less throughout the class, as well as in Fishes. Besides the Ruminants, several different orders or families of Mammalia have a sheath of this striated fibre extending all along the oesophagus to or even on the cardia, as may be well seen, for example, in Rodents, Rears, and many others; while this kind of muscle in Man, Quadrumana, Felidae, the Horse, and several more Mammalia stops on the oesophagus much short of its cardiac end. The comparison of the muscular coat of the oesophagus of Owls, and other Raptorial Birds that regurgitate their food in "castings," with the corresponding sheath in Ruminants is erroneous ; for this sheath is deficient in the striated muscular fibre in Owls and other birds, while striated muscle composes the chief portion of the coat of the oesophagus of Ruminants. Though numberless observations may be required to obtain and methodize all the facts, very easy and simple examinations will suffice for single diagnoses ; just as, by an inspection of one part, we can arrive at the whole character of a plant or animal which had originally been determined by far more extensive researches. Constant differences in morphological arrangements are not the less important because we happen to be ignorant of their meaning. To define the exact value in taxonomy of the muscular sheath of the oesophagus requires far more extensive researches than I have been able to complete; but my observations show that it eertainly affords valuable characters. Comparative anatomists have long since perceived many resemblances between birds and reptiles ; and of late Professor Huxley (Proc. Zool. Soc. 1867, p. 415 et seq.) has so more particularly determined the characters common to these two classes as to form them into his one great group of " Sauropsida." Accordingly he describes more exactly and comprehensively than had been previously done those points in which the two classes, constituting that one primary group, agree together and differ from Mammalia. But both he and his predecessors have neglected the oesophageal sheath, although it appears probable, from the observation cited above, that this presents good characteristics. In short, in those observations the transversely striated muscular |