302 THE ALIMENTARY TRACT, ETC. 



blood-vessels. The larger ducts have an especially rich supply of 

 nerves, of which fibrils may be traced towards the ciliated epithe- 

 lium ; an anatomical connection between the two has aiot, however, 

 been made ont.] 



III. THE SPLEEN. 



a. General description. Although the spleen belongs to the 

 lymphatic system, it is considered here in order to complete the 

 description of the abdominal viscera. It is a small, rounded-oval 

 body, of a reddish-brown colour, suspended in the mesentery near 

 the anterior end of the large intestine (Fig. 184 M.:). In medium- 

 sized animals the longer diameter is about 6 mm., and is parallel 

 with the long axis of the body; the shorter diameter is about 

 5 mm., and the thickness varies from about 3 mm. to 4 mm. 

 The dorsal surface is flat or slightly concave [Hi I us lieiils), and re- 

 ceives the relatively large afferent and efferent vessels ; the rest of 

 the organ is smooth and rounded, and with its greatest convexity 

 directed towards the left side. 



b. [Minute structure. The structure of the spleen resembles 

 that of higher animals. It possesses a serous coat of peritoneum, 

 under which is a fibrous coat ; the latter sends in trabeculae, 

 which divide and form a fine meshwork of supporting-tissue ; the 

 finest trabeculae are formed by the processes of the connective-cells 

 of the sustentacular structure. According to Hoffmann, the thick- 

 ness of the fibres averages o'ooi to O'oii mm.; the intervening 

 spaces measure 0'002 to o"Oi2 mm. The spaces are filled by the 

 spleen pulp, which consists of true spleen-corpuscles, blood-cor- 

 puscles, and pigment-corpuscles. 



The spleen-corpuscles have an average diameter of 0'Co6 mm., 

 and are round or of a rounded oval form. Each consists of a nucleus, 

 with a very small amount of adherent protoplasm ; the nucleus 

 possesses one or two nucleoli. Some of these cells contain a 

 brownish or black pigment in granules, but most of them are 

 colourless (Hoffmann). 



The pigment-cells equal the white blood-corpviscles in size, and 

 exactly resemble the corresponding pigment-cells of the liver. 



The blood-corpuscles are found in various stages of disintegra- 

 tion and rcii'eneration. 



