78 GENERAL ANATOMY OF THE TISSUES. 



distinguish two types which correspond with its two principal 

 forms, the solid and the areolated. The former is developed 

 out of masses of cells without any demonstrable matrix, bv the 

 elongation of the cells, their breaking up into fibrils, and their 

 coalescence. This is most obvious in the tendons and liga- 

 ments, which, as observations upon Batrachian larvse and upon 

 mammalian embrvos show, at first consist entirely of com- 

 mon, rounded, formative cells, which about the same time 

 as the transversely striated muscles are formed, (in mammalia 

 in the second month) become fusiform. The further develop- 

 ment demonstrates (what had escaped Schwann) that only one 

 portion of these fusiform cells, and in fact cells which are re- 

 markable for their size and paler contours, become bundles of 

 connective tissue, while the others, which Schwann in part 

 depicts rightly (Tab. Ill, fig. 11 ; the smallest cell, fig. 6, from 

 connective tissue, the cell b, and the lowest cell upon 

 the right side), remain for a time as fusiform elements, and 

 only subsequently become fused into elastic fibres. There 

 arises, at last, out of cells alone, with no distinguishable 

 matrix, a compact tissue composed of two chemically quite 

 distinct fibres. The areolated connective tissue differs from 

 the former in the circumstance that, if not from the beginning 

 yet from the time at which the cells become elongated, an 

 abundant gelatinous intermediate substance is developed be- 

 tween them, which does not yield gelatine, and never becomes 

 converted into it, but contains albumen and a substance similar 

 to mucus ; Schwann, indeed, found a substance resembling 

 pyin, in this tissue. Although all embryologists know that the 

 areolated connective tissue is at first of a gelatinous consistence, 

 as, for example, under the skin, in the neck, in the omentum, 

 behind the peritoneum, in the orbit, and in the bones, no one 

 has yet drawn attention to the general occurrence of that inter- 

 mediate substance which was observed by Schwann in a single 

 locality. I originally became acquainted with this tissue be- 

 tween the chorion and amnion, and at first paid more attention 

 to its reticulated anastomosing cells. Subsequently, when I 

 examined it more closely in the enamel organ of the em- 

 bryonic tooth sac, I paid attention to the peculiar intermediate 

 substance, and at the same time Virchow described this tissue 

 from the \imbilical cord, where the gelatinous tissue of Wharton 



