350 The Development of the Connective Tissues 



the intermuscular septa, ligaments, superficial fascia, and cutis, the least 

 development being immediately helow the epidermis. Even here it is no 

 longer typical syncytium, but partly differentiated. The process con- 

 tinues in embryos 9, 10 and 12 cm. long; most of the prefibrous tissue 

 is still within the syncytium. Immediately over the muscle a further 

 differentiation of the prefibrous tissue of the perimysium has taken 

 place. In this narrow zone the fibrils are arranged in parallel bundles 

 apparently communicating with one another as well as being continuous 

 with the neighboring exoplasm. In this region the individual fibrils 

 anastomose with one another. Prefibrous tissue is changing into fibrous 

 tissue very rapidly in an embryo 16 cm. long. The perimysium, com- 

 posed of parallel fibers, sends processes of wavy fibers into the super- 

 ficial fascia, and from them fibers enter the cutis. All of the tissue 

 between the epidermis and the underlying muscle is composed of these 



^ " '-^ 9 -^:' ^ ^ f 



^- ^ ^ 



Fig. 12. Fig. 13. 



Fig. 12. Section through the skin of a pig 5 cm. long ( x 250 diameters). The first 

 white fibers are just forming in the exoplasm. 



Fig. 13. Section through the skin of a pig 16 cm. long ( x 250 diameters). The 

 nuclei and endoplasm on the left are immediately below the root of a hair. 



wavy fibers, either isolated or connected with the exoplasm, which 

 is very fibrillated. The process is quite complete in embryos from 20 

 to 30 cm. long. In the older embryos, however, the density of the 

 fibers is greater in the skin than in the underlying superficial fascia. 



The individual fibrils after once well formed are of unequal size, 

 often appearing in bands and frequently anastomosing. The anasto- 

 moses are finally broken and the bands and thicker fibers split into the 

 individual fibrils. 



I have now followed the development of the white fibers from the 

 exoplasm of the sj'ncytium without considering the nuclei and the 

 endoplasm. What follows relates to them. 



In smaller embryos (2 cm.), which have been stained by Mallory's 

 method, the nuclei are round or oval with a small amount of endoplasm 

 around them. When the tissue is macerated in Miiller's fluid for 24 



