CAECUM OF RABBIT. 29 



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 vermi- 

 form 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 caput 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. 



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, /. ., and Hand- 

 buch der Histologie 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 

 Strieker'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, /. c. p. 65. 



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

 Fig. i. 



