TISSUES OF THE BODY. 283 



termination of the rectum; it is met with also in the mucous membrane 

 itself, as the so-called muscularis mucosce, in the form of thin layers and 

 small bundles. The organs of respiration are likewise supplied with this 

 tissue : thus, it is seen in the posterior wall of the trachea, in the circular 

 fibres of the bronchi and their branches, and perhaps also in the pul- 

 monary vesicles. The walls of blood-vessels possess it also, especially in 

 the middle layer of their coats. These contractile cells make their appear- 

 ance too in the cutis: firstly, in the form of small groups, as in the 

 hair follicles, the sebaceous and sudoriferous glands; and then again 

 forming more or less continuous layers, as in the tunica dartos of the 

 scrotum, the mamma, and areola. The human biliary apparatus only 

 shows tissue in the walls of the gall bladder (Henle, Eberth}. Further, 

 the tissue is distributed throughout the urinary apparatus. It occurs in 

 the calyces of the kidneys in the form of continuous strata, and also in 

 the pelvis of the latter organ, in the ureters and vesica. Again, in the 

 form of scattered elements along the urethra and over the surface of the 

 kidney. In the male organs of generation also it is extensively met 

 with : thus, in the tunica dartos, between the tunica vaginalis communis 

 andpropria of the cord, epididymis, vas deferens, seminal vesicles, prostate, 

 Cowper's glands, and corpora cavernosa. Also in the female : thus, in the 

 ovaries, in the Fallopian tubes, and uterus, which latter organ presents to 

 us during pregnancy the greatest accumulation of the tissue in question 

 which exists in the bo.dy. Again, in the round (Koelliker] and broad 

 ligaments (Luschka), and in the corpora cavernosa. Further, smooth 

 muscular fibres are supposed to exist in the envelope and in the septa within 

 the spleen and lymphatic glands of mammals. Finally, they occur in the 

 organs of vision as sphincters and dilators of the pupil ; also in the choroid, 

 in the ciliary and orbital, as well as eyelid muscles (H. Miiller). 



164. 



The second species of muscular tissue, namely, the sftiped or 

 striated,, is to be found in all the muscles of the trunk and extremities, 

 those of the ear and external parts of the eye, with the exception of 

 the muscles mentioned in the preceding section. It enters further into the 

 construction of many internal organs, as the tongue, pharynx, upper portion 

 of oesophagus, larynx, genitals, termination of the rectum, and diaphragm. 

 Finally, it presents itself, modified to a certain extent, in the heart. 



As elements, we here meet with long cylindrical and strongly flattened 

 fibres (fig. 274, 1), which do not, as a rule, give off branches. They 

 have a thickness of from 0'0113 and 0*0187 mm. up to 0'0563 mm. in 

 the human body. To these the name of " muscle fibres " or " primitive 

 bundles " has been given. The human primitive bundle, which is, owing 

 to its greater thickness, of a yellower tint than the smooth element, dis- 

 plays, in 'contrast to the latter, a most striking and characteristic texture 

 under high magnifying power. 



It consists of an envelope and contractile contents. The first of these, 

 called usually the " sarkolemma " or " primitive sheath," is a transparent, 

 homogeneous membrane, which, on account of its high degree of elasticity, 

 always remains closely adherent to the included mass in all the changes 

 of form which take place in the latter (fig. 274, 1). The primitive 

 sheath may be demonstrated apart from chemical aid by simply break- 

 ing the continuity of the contents (2 a), or also, as is strongly recom- 

 mended, by treatment of the living fibre with water, on which the 



