232 Caroline McGill, 



brates, has described protoplasmic connection not only between smooth 

 muscle cells, but also between muscle cells on the one hand and epi- 

 thelium, ganglion cells, and connective tissue cells on the other. 



The muscle syncytium in the smooth muscle of the adult pig is 

 made up of the much elongated muscle nuclei, with surrounding pro- 

 toplasm, including the myoflbrillae. Immediately surrounding the nucleus 

 a small amount of granular protoplasm is often visible (Fig. 22). 

 This may be greater in amount and extend out among the myofibrillae. 

 The main mass of the muscle cell consists of the myofibrillae, which 

 tend to be arranged in spindles around the individual muscle nuclei, 

 thus forming the so-called smooth muscle fibers. Many fibrillae, however, 

 run in broad bundles into neighboring muscle cells thus establishing 

 intimate protoplasmic continuity (Fig. 22, pb). Then also in many 

 places more delicate protoplasmic strands connect the muscle fibers 

 together (Fig. 21, ph). If Figs. 16 and 18 are compared with Figs. 25, 

 26 and 29, it will be seen that in the adult the myofibrillae are 

 arranged in more definite, compact bundles than in the foetus. 



The muscle nuclei in some places show as very much elongated 

 rods (Fig. 21). This is the usual condition when the spindles are 

 elongated. Where the tissue is more loosely arranged, as in Fig. 22, 

 the nuclei are often of spiral form. Investigators of the contractility 

 of adult smooth muscle have taken the spiral nucleus as a criterion 

 of contracted muscle. This can hardly be considered as definitely 

 established, however. 



In the adult, as in development, two kinds of myofibrillae are 

 present: 1. very fine fibrillae, evidently corresponding to the „elemen- 

 tary" fibrillae of Apathy (1890 and 1891) and to the „Binnenfibrillen" 

 of Heidenhain; and 2. coarse fibrillae which seem to correspond to the 

 „primitive" fibrillae of Apathy. The latter in some particulars also 

 resemble the „Grenzfibrillen" of Heidenhain (1898 and 1900) in others 

 more closely the „myofibrils" of Benda (1902). 



The fine myofibrillae become very numerous in the later foetal 

 stages, and in the adult the muscle cell is usually well filled with them. 

 They are often the only myofibrillae present (Plate XI, Fig. 22, ff). 

 They are apparently homogeneous structures. They stain more intensely 



