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Show 610 MR. G. W. BUTLER ON THE [Dec. 3, between them and the abdominal cavity is accounted for by it being a part of the muscular abdominal wall, separated from the outer layer by the spaces surrounding the subcutaneous fat. In birds, again, besides the subperitoneal fat of the " omentum," we have subcutaneous fat along the whole length of the trunk, on each side of tbe thorax and abdomen, and this extends on to the legs. This series of deposits is well seen in the unhatched chick. Doubtless subcutaneous fat is found in the above-named groups, in places besides those indicated, which, however, are those which I have specially studied in examining the interesting questions raised by Beddard's papers; but, as a general rule, not only in the above groups but also in mammals such subcutaneous fat is characteristic of the morphologically ventral face of the body rather thau of the dorsal. Moreover the deposits in mammals seem largely to correspond with those in the Sauropsida. Nor is the degree of constancy of distribution of these subperitoneal and subcutaneous fat-deposits which exists surprising, if, as I think, this distribution is connected with that of the blood-vessels **. VI. ON THE FATTY "SPLEEN " OF THE CROCODILES. I should like to draw attention to a curious body which seems very constant in all specimens of Crocodile. It is situated on the right side and is attached dorsally by a distinct peritoneal ligament, which extends obliquely from near the externo-posterior extremity of the right liver-lobe, to a spot more median than the anterior end of the reproductive gland (cf. above, Plate XLIX. fig. 43, with the '' seeker'' represented). The only references to this body that I have seen occur in Hunter's ** Essays and Observations,' edited by Owen (vol. ii. p. 338), and in Owen's papers in this Journal for 1831, pp. 141 and 169. Hunter describes it as the spleen. Owing to the intestines being much folded, it is quite possible that this distinctly dextral body may be in the morphologically normal position of the spleen, i. e. suspended on the left side of the median membrane that supports the alimentary canal. But, on the other hand, as Hunter remarked (loc. cit. p. 339), there is " an oblong dark body placed in the root of the mesentery;" he says further on, " 1 imagine this is 1 The ventral region of the body above referred to is, of course, the region where the mammary glands are apt to occur. These are generally allowed to be specialized cutaneous (sebaceous) glands, and they are described by Dr. Creigbton (Journ. Anat. & Phys. TOI. xi.) as arising in intimate association with deposits of fat. N o w the femoral glands of Lizards open on the ventral side of the abdomen and thighs, and are frequently found surrounded by fat, and in microscopic sections strongly resemble sebaceous glands. Gegenbaur has recently shown that in tbe Monotremes the mammary glands do not conform to the type common to all the higher Mammalia, and yet we place the two types of gland in the same category; may it not somewhat similarly be suggested that in these quasi-sebaceous glands of lizards, and deposits of ventral subcutaneous fat, so commonly represented in Birds and Eeptiles, we have the Sauropsidan modification of that which in Mammalia has developed into such typical structures as the mammary glands and the sebaceous glands in association with which the characteristic hair occurs ? |