COMMON RAT. 



In the middle line of the body inferiorly to the heart we see 

 surfaces of the six sternal bones, and in the angle intercepted between the 

 lowermost of these and the diaphragm, we see some lobules of fatty tissue 

 set in the process of serous membrane which connects the apex of the 

 pericardium with the sternal bones and with the diaphragm. From these 

 structures a vein passes back along the pericardium to end in the vena 

 cava descendens of the left side. 



In the angle between the Inferior surface of the diaphragm and the 

 lumbar muscles, the two psoas muscles and the quadratus lumborum of the 

 left side, we see the smooth-surfaced kidney, which by this external 

 character, as also by the internal one, of the separation of its cortical or 

 secretory from its medullary or excretory parts, characterizes the class 

 Mammalia. The spleen is in relation with it on the right ; to the right of 

 the spleen we have the left end of the stomach, which is less vascular and 

 glandular than the pyloric half, here concealed and overlapped by the left 

 lobe of the liver. From the inferior or convex margin of the stomach the 

 curtain-like omentum^ a process of peritoneum found, thus developed, only 

 in mammals, hangs down over the left cornu of the uterus, which is dis- 

 tended with embryos, and over portions of the intestines. Immediately 

 below the kidney and the spleen, the left ovary and Fallopian tube and the 

 upper end of the left cornu uteri are situated. A fibrous band, under which 

 a black bristle is placed, and which is the remnant of the ligament by which 

 the Wolfftan body in the foetus was kept in relation with the diaphragm, 

 attaches the ovary and tube to the peritoneal covering of that muscle. 

 Below the upper end of the left cornu uteri is seen the caecum, which is of 

 less size and complexity than that of Rodents with rootless molars and less 

 varied and nutritious food than these omnivorous members of the order, or 

 than that of those, such as the Squirrels, which live on seeds and have, like 

 most Mnridae, rooted molars. It tapers off superiorly into the large intes- 

 tine, which however in many Rodents is not, when compared with the 

 small intestine, as much inferior in length and larger in calibre and thicker 

 in its walls as its name and the homology of anthropotomy might lead 

 us to expect. Below the caecum we see the cut ends of the veins from the 

 hind-limb, and lower still we see a bristle passed underneath the ureter as 

 it passes forwards to enter the base of the conically contracted bladder. 

 The vagina, rectum, and bladder have, each of them, separate and indepen- 

 dent outlets ; into those from the two latter organs black bristles have been 

 passed. The flat nail on the rudimentary thumb ; the presence of tactile 

 vibrissae above the eyes as well as upon the snout ; and of hairs of great 

 coarseness along the mesial dorsal region ; the absence of hair from a small 

 area, bifid, as usual in Rodents, in which are the orifices of the nostrils, and 

 which is called the ' muffle ; ' and its presence between the annulate scales 

 on the tail ; are points worthy of notice. 



B 2 



