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Show 1894.] VISCERAL ANATOMY OF ORNITHORHYNCHUS. 717 ceivably be a variable structure. The auimal, after havingbsaa skinned, was carefully opened to the left of the middle line so as not to interfere with any structures which might be there. I found in the middle ventral line a fold of thin membrane depending from the parietes into the body-cavity. This fold was crumpled up, but could be readily extended and was then seen to be fully a quarter of au inch in diameter. This fold was attached posteriorly to the bladder, and anteriorly became continuous with the falciform ligament of the liver. This fold must, I think, be regarded as the remains of the primitive ventral mesentery. I strongly suspect, but have unfortunately an insufficient recollection of the facts to confirm m y suspicions, that a similar fold exists in Echidna. That it should be anangious in the one case and bear a bloodvessel in the other is interesting but not unintelligible. To quote one out of many analogous instances, certain of the mesenteries supporting the caecum in the Lemurs may or may not have bloodvessels x. The Alimentary viscera have been described by so many authors, including H o m e , Meckel3, and Owen4 , that I can limit myself to a very few remarks. The expression " de grandeur moyenne," applied by Meckel to the stomach5, and repeated by Sir B. Owen 8, is less applicable to the stomach which I examined than the expression used by the translators of Meckel, viz. " extre-mement petit." In Meckel's original figure, copied by O w e n in the ' Comparative Anatomy,' the dimensions are too great. I found the greatest diameter of the stomach to be 1| inch (exactly Sir E. Home's measurement), as against 5 feet 4 inches total length of alimentary canal. W h e n the viscera were fully displayed by cutting and reflecting the abdominal parietes, the omentum was seen to extend right back to the pelvic region. It is attached to about the last four inches of the large intestine. The slender caecum is about one inch long and is about 11 inches from the cloaca. The valvulae conniventes of the small intestine have been figured by Meckel; but as his figures are a little rough and do not quite do justice to the structures, I have thought it worth while to have the accompanying drawing prepared (fig. 1, p. 718). At about the distance of one foot from the caecum the valvulae conniventes come to an end. Their termination is rather more abrupt than I should have supposed from 1 Beddard, " Additional Notes upon Hapalemur griseus," P. Z. S. 1891, p. 451 et seqq. 2 " A Description of the Anatomy of the Ornithorhynchus paradoxus," Phil. Trans. 1802, p. 67. 3 Omithorhynchi paradoxi descriptio anatomica. * " O n the Young of the Ornithorhynchus paradoxus, Blum.," Tr. Z. S. vol. i. p. 221 6 ' Traite" genera! d'Anatomie Comparee,' Trad. Fr. (Paris, 1838), vol. viii. p. 539. B * Comparative Anatomy of Vertebrates' (London, 1868), vol. iii. p. 410. |