With Figure 3.

THE lymphatic (or lacteal) sinuses 1 surrounding the Peyerian follicles in the walls of the vermiform appendix, a, in the dilated termination of the small intestine, c, and in a saucer-shaped patch of glands, d, in the large intestine, have been injected with Berlin blue, so as to show the relation of the lacteal vessels to the Peyerian follicles in the walls of the intestine, as also to certain mesenteric glands left in relation with it. The mesentery connecting the caecum and vermiform appendix with the segments of the small and large intestine has been cut through, and the caecum disposed so as to form the periphery of the preparation. The centre-point of the preparation and of the figure is occupied by a globular sac, c, the 'sacculus rotundus' the thick walls of which consist of Peyerian follicles, and represent the histologically somewhat similar termination of the small intestine in man. The small intestine dilates to form this sac after describing a siphon-shaped course internal to one formed by the commencement of the colon. A saucer-shaped patch, d, similar in structure to the sacculus rotundus, lies immediately to the right of it in the wall of the large intestine, and overlies the opening of the ileocaecal valve.

The caecum consists of two parts: the first of them, b, 14.5" in length, is wide in calibre, diminishing somewhat towards its termination, thin in its walls, and spirally constricted externally in correspondence with the spiral valve developed internally; the second, a, about 5.5" long and corresponding to the vermiform appendix of anthropotomy, is of much smaller calibre, but of much thicker walls, consisting mainly of Peyerian follicles; it has no internally projecting fold nor externally impressed furrows, but is mapped into well-defined spaces by the injection occupying the lacunar spaces of the Peyerian patches. This injection may be seen to have passed into some mesenteric glands attached to the spirally-constricted portion of the caecum close to its junction with the appendix. What may be called the capttt coli lies in this preparation between the concavity of the caecum and the two Peyerian agglomerations of glands already mentioned. Its external surface is not puckered or corrugated, but from it the three longitudinal muscular bands, the so-called taeniae coli, take origin and give a sacculated appearance to the commencement of the colon proper.

The mucous membrane of the colon is seen to be beset with villi of a granulation-like appearance, an unusual appearance in Mammalia. The inwardly projecting folds of the colon are, the spiral coils of the caecum are not, obliterated by distension. From this Preparation and Figure it may be seen that the Peyerian agminate glands may take either the form of a caecal cylinder with thick walls as in the vermiform appendix, a, here and in man; or that of a globular sac such as that developed here at c immediately proximally to the ileocaecal valve; or that of a saucer-shaped thickening of the walls of the large intestine immediately beyond that valve. In like manner the follicles, which are the essentially distinctive characteristic of the Peyerian 'patches' are themselves found, when examined under low powers of the microscope, to be of very various shapes; those, for example, from the vermiform appendix of the Rabbit presenting the outlines of the sole of a shoe, whilst those of the Guinea-pig and of Man are subspheroidal in shape.

1 The lymphatic and lacteal vessels of many organs may be readily injected by the simple 'Einstichsverfahren' of Hyrtl and Teichmann. It is especially easy to obtain successful results in the case of the Peyerian glands of the Rabbit where, as in Bos and Ovis, the base of the follicles is surrounded by lymphatic sinuses, and not as in man and in the Carnivora by a reticulation of lymphatic vessels.

(Half natural size.) Caecum with Vermiform Appendix and parts of large

Fig. 3. - (Half natural size.) Caecum with Vermiform Appendix and parts of large And Small Intestine Of Rabbit (Lepus cuniculus).

a. Vermiform appendix.

b. Thin-walled portion of caecum, spirally constricted in correspondence with an internally situated spiral valve.

c. The sacculus rotundus, or dilated globular end of small intestine, with thick walls consisting of Peyerian follicles.

d. Saucer-shaped thickening of wall of large intestine, on the internal periphery of which, not shown in this figure, the ileo-caecal valve opens.

e. Distal end, i. e. segment next caecum, of small intestine in section. f. Proximal end, i. e. segment next caecum, of large intestine in section.

Attached to the spirally-constricted part of the caecum on its inner edge, just before it passes into the vermiform appendix, we see certain mesenteric glands into which an injection of Berlin Blue has passed, having been introduced by 'Einstichung' or puncture with a fine syringe into the lacunar spaces surrounding the Peyerian follicles of the vermiform appendix.

For a description of the caecum and the sacculus rotundus, see F. Bohm, De Glandularum intestinalium structura penitiori, Berolin. 1835, Diss. inaug., cited Frey, Z. W. Z. xiii. p. 28, .1863.

For the histology of the Peyerian glands generally, see Frey, l. c., and Hand-buch der Histologic et Histochemie des Menschen, ed. 5, 1876, p. 525 (lit. p. 529); His, Z. W. Z. x. p. 333; xi. p. 416; xiii. p. 455.

For the histology of a Peyer's patch in small intestine of Rabbit, see Verson in Stricker's Histology, Eng. Trans, vol. i. p. 566, fig. 108.

For that of the sacculus rotundus, see His, Z. W. Z. xi. p. 426, Taf. xxxv. Fig. 6; Frey, l. c. p. 65.

For that of the vermiform appendix, see Frey, Z. W. Z. xiii. p. 64, Taf. iii. Fig. 1.

For that of the Peyerian patch on the colon, where the follicles are larger than anywhere else, see Frey, ibid. p. 68.

For the method of injection by puncture and the use of Berlin blue, see Frey, Z. W. Z. l. c. p. 52, and Mikroskopische Technik, ed. 7, 1881, pp. 128, 132, 293, 295; and Schafer, Practical Histology, pp. 144 and 157.

For the presence of villi in the large intestine, see Cuvier, Lecons, ed. 2, 1835, iv. pt. 2, pp. 243 and 274.