328 GENERAL CONSIDERATIONS ON THE DIGESTIVE APPARATUS. 



(UnstripedoT smooth bands of muscles are composed of long fusiform cells 

 with staff-shaped, elongated nuclei, the cells varying from l-1125th to l-50th 

 of an inch in length, and from l-5625th to l-1125th of an inch in breadth.) 



Fig. 146. 



CONICAL VILLI ON MUCOUS MEM- 

 BRANE OF SMALL INTESTINE; 



MAGNIFIED 19 DIAMETERS. 



a, Zone of follicles surrounding a soli- 

 tary gland ; 6, Apertures of simple 

 follicles. 



Fig. 147. 



FUSIFORM CELLS OF SMOOTH 

 MUSCULAR FIBRE. 



c. When the organs are lodged in one of 

 the great splanchnic cavities, such as the 

 chest or abdomen, they have a third mem- 

 brane a serous layer, which lines the cavity, 

 and is reflected around the viscera contained 

 in it, so as to envelop them more or less 

 completely. This layer has, therefore, an 

 adherent face, applied either against the walls 

 of the cavity or the external surface of the 

 splanchnic organs ; and a free face always in 

 contact with itself. 



A serous membrane is composed of two 

 layers : a deep, connective portion, analogous to 

 the mucous corium ; and a superficial, which is 

 only pavement epithelium. The free surface 

 of this epithelium is perfectly smooth, and 

 lubricated by a limpid serosity to facilitate the 

 gliding of the parts the membrane covers. 

 (The epithelium is a simple tesselated layer 

 of flattened and polygonal nucleated cells, 

 about 1 1200th of an inch in diameter). 



2. The solid organs are either contained 

 in the splanchnic cavities or situated outside 

 them, in the midst of connective tissue, which, 

 in condensing around them, often forms a 

 fibrous covering. 



Like the hollow organs, they are single 

 spleen', liver ; or in pairs kidneys ; and 

 symmetrical or asymmetrical. They are 

 retained in their situation by their vessels 

 and nerves, by adherence to the neighbouring 

 organs, or by particular serous attachments. 



With the exception of the lungs of animals 

 that have respired, all the solid organs have a 

 density greater than water. Their weight and 

 volume offer numerous differences, which are 

 individual or relating to the species to which 

 they belong. Nevertheless, each organ pos- 

 sesses a certain volume and weight which 

 might be termed physiologic ; when the organ 

 is above or below this average, we are 

 authorized in saying that it is in a patho- 

 logical condition. 



Organs are more or less round inform, 

 and their surface is traversed by a variable 

 number of furrows which indicate their 

 division into lobes or lobules. 



a, Two cells in their natural state, one showing the staff-shaped nucleus ; b, A cell 

 with its nucleus, c, brought distinctly into view by acetic acid. 



