Dissection of Common Rat, 191 



bristle passed into the ' common ' duct from its opening into 

 the Intestine ; and the villous coating noted, a small portion 

 being placed under a low power of the microscope. 



The student should next direct his attention to the division 

 of large and small Intestines, marked by the presence of the 

 CcBCum^ or head of the colon {caput ccecum coli) viz. the rounded 

 pouch-like projection of the large Intestine, which receives, at 

 about an inch from its blind extremity, the termination of 

 the small Intestine. The Caecum should be cut open by mak- 

 ing a window in the side opposite the entrance of the small 

 Intestine, and making two incisions, one along the attached 

 border of small Intestine to meet this aperture ; and the other, 

 opening the large Intestine, towards the same direction. The 

 absence of internal septa, dividing it into cells*, so commonly 

 found in Rodentsf will be noted ; as also, on the contrary, its 

 simple form and moderate size, which appears to be correl- 

 lated in this Order, with rooted tubercular molars, and a non- 

 exclusive vegetable diet. The Caecum is bounded towards 

 the small Intestines by a tumid white ring, representing the 

 ileocaecal valve, close to which is the commencement of the 

 large Intestine marked by longitudinal rugae and the absence 

 of villi ; the calibre of the large Intestine is about half that 

 of the Caecum. The longitudinal rugae do not extend beyond 

 three inches from the Pylorus ; after which the Intestine be- 

 comes both thinner and even- surfaced, except a slight pucker 

 here and there where a bend occurs. 



Portions of the Small Intestine above the CcECum (for 

 Peyer's glands) ; of the Caecum itself ; and of the Large In- 

 testine, one piece taken near to the Caecum, and another near 

 to the Pectum, should be put under the microscope, in order 

 to see well the difference of the mucous lining. 



The Intestines should now be separated from the mesentery, 



* e.g. The spiral membrame found in the Hare ; or the honeycomb arrange- 

 ment ef the walls found in other species, 

 t Waterhouse. 



