MUSCULAR FIBRE-CELLS. 387 



Distribution of Muscular Fibre- Cells. 



The smallest forms of these cells are found in the walls of the 

 smallest arteries and veins, and the larger lymphatics. The follow- 

 ing general account of the distribution of all their forms is from 

 Kolliker. It should, however, be premised that this kind of mus- 

 cular tissue never forms isolated muscles in the human body. The 

 fibres are either scattered in the areolar tissue, or form membranous 

 expansions as the muscular layer of the bladder and alimentary 

 canal ; and in either case the fasciculi are either parallel, or woven 

 into a network. 



1. In the alimentary canal, these fibre-cells form the muscular 

 coat (tunica musculosa), from the lower half of the oesophagus, 

 where striated fibres are mixed with them, to the internal sphincter 

 ani. They also form the muscular layer of the mucous membrane 

 from the pylorus to the anus in man, and constitute the scattered 

 fasciculi in the villi. 



2. In the air-passages, a layer of contractile fibre-cells (smooth 

 muscular fibres), exists in the posterior wall of the trachea, and 

 extends through the bronchial tubes to their finest subdivisions, as 

 a complete muscular membrane. 



3. In the urinary organs, the smooth fibres were first found to 

 extend throughout the male urethra by Mr. Hancock, of London. 

 They also form two distinct layers in the bladder, and a layer ex- 

 tending through the ureters into the pelvis of the kidney. 



4. In the male sexual organs, they are found in the dartos, exter- 

 nally to the tunica vaginalis, in the vas deferens, the vesiculse semi- 

 nales, the prostate, around Cowper's glands, and in the corpora 

 cavernosa penis, and the subcutaneous areolar tissue of this organ. 



5. The female sexual organs contain the smooth muscular fibres 

 in the corpora cavernosa of the clitoris, the vagina, the uterus 

 (where they become even ^ of an inch long during pregnancy), in 

 the Fallopian tubes, in different places in the broad ligaments of 

 the uterus, in the round ligaments, and those of the ovaries. They 

 also exist in the areolae of the lacteal glands, and the nipples. 



6. In the vascular system, these fibre-cells exist in the middle coat 

 of all, and most in the smaller, arteries ; and in that of most veins, 

 and of the lymphatics, except the finest ; also in the lymphatic 

 glands of some lower animals (Heyfelder) ; and the external tunic 



