ELEMENTARY FORMS. 29 



The tendinous expansion of the Diaphragm. 



The membrana tympani. 



The valves in the heart, the veins, and in the lymphatics. 



The neurilemma, that is, the envelope which surrounds the nerves. . 



The fasciae. They are developed from the amorphous layers of uniting 

 tissue like membranes, and envelope the muscles passing into the intermus- 

 cular ligaments, and from these into the periosteum (ligament. Cruriata), or 

 into the tendons of muscles (fasc, red. abdomin.') 



Periosteum (membrane covering the bones), and Perichondrium (that cover- 

 ing the cartilages). They surround the bones and cartilages externally, and 

 are attached to these, from the first, by the extremely numerous vessels 

 connected together by areolar tissue, of which they consist. In the cavity of 

 the bones the periosteum is with difficulty separated from the epithelium 

 lying upon it. 



5. Tunica propria of the intestinal canal, of the gall and urinary bladders, 

 the pelvis of the kidneys, the ureters, &c., is a peculiar membrane (T. nervea, 

 vasculosa) of uniting tissue, which lies between the muscular layer and mu- 

 cous membrane ; shining white ; almost inseparably connected, externally, 

 with the uniting tissue of the muscles ; internally, with that of the mucous 

 membrane. 



6. Serous membranes. They serve as the boundaries of cavities inside 

 the body, and are generally quite closed. Henle makes a distinction between 

 true, that is, such as are covered on the outside with (pavement) epithelium, 

 and false, in which it is wanting. 



To the false belong the Burste Mucosa of muscles, tendons, and mem- 

 branes ; these are closed sacs, filled with watery or viscous fluid, which lie 

 between muscles and bones (capsulce synoviales). 



The true serous membranes consist of a layer of Epithelium (generally 

 pavement, only in the tubes of the Uterus ciliated), and of fibrous uniting 

 tissue, which approaches at one time fibrous, at another time elastic tissue. 

 The separation of the subserous uniting tissue is, almost in all cases, only 

 artificial. 



They not only serve for lining cavities, but also as the envelopes of the 

 organs which lie in them. But it is not essential that they should be, every- 

 where, entirely closed. (The peritoneum of the female is open at the extre- 

 mities of the Fallopian tubes.) 



To this class belong: Plura and Peritoneum, Pericardium, Arachnoidea, 

 Tunica Vaginalis. They lie in the cavities as sacs, the external surface of 

 which is attached by plain uniting tissue, partly to the. walls of the cavities, 

 partly passing over upon the organs, which forms a sort of inversion of it ; 

 the internal surface is smooth, covered with pavement epithelium, and se- 

 cretes a thin, watery, albuminous fluid, Serum. 



The sacs form folds, ligaments, and rete, particularly at the places where 

 the vessels and nerves are allowed a free thoroughfare to the organs enveloped 

 by them. The vessels and nerves become, therefore, covered by uniting tissue 

 and epithelium, but they do not perforate the serous sacs. 



The serous membranes do not pass merely into fibrous, but also into mucous 

 membranes (e. g., mucous membrane of the tympanic cavity). 



7. The vascular membrane of the brain (Pia Mater), and that of the eye 

 (Choroidea), that is, a membranous uniting tissue as a support for vessels 

 which nourish another organ. Pia Mater, like periosteum, is firmly connected 

 with the brain, into which its vessels penetrate, and consists of loose bundles. 

 Choroidea resembles the Corium, which serves as a Matrix for the Epidermis. 



