80 HISTOLOGY. 



They are certainly closely invested by connective tissue membranes or net- 

 works (Fig. 92), consisting of white and elastic elements and extending from 

 cell to cell. These may be formed from the protoplasmic processes of the 

 mesenchymal muscle cells, or from distinct interspersed connective tissue 

 cells. Tissue spaces exist in this network between the muscle fibers. 

 The loose muscular coat of the blood vessels in the umbilical cord is a 

 particularly favorable place for the study of fibrous tissue in relation to 

 smooth muscle. 



In ordinary sections the student should recognize smooth muscle 

 by the parallel arrangement of its cells, with which the nuclei correspond, 

 and by the protoplasmic appearance of muscle substance as compared 

 with fibrous connective tissue. In doubtful cases Mallory's connective 

 tissue stain may be used, making the muscle substance red and the white 

 fiber blue. In cross section smooth muscle appears as in Fig. 93. Since 

 the cells taper the sections near their ends are smaller than the others. 

 Only those cut near their centers show nuclei. Between groups of muscle 



cells there are generally bands of 

 ,,ov^-^ r ^ connective tissue containing lym- 



Connective tissue ^UhT>r^T^d? 



septum. ^IX^rDpCJS?^ phatic and blood vessels, and nerves 



which terminate in contact with the 



smooth muscle fibers ) -MM-Zo^Vw^W cells in a manner to be considered 



and nuclei in cross > TT>LlV_"-<O-' ' T i i 



section. j p^^p~' later. In describing smooth muscle 



FIG. 93. SECTION OP THE CIRCULAR MUSCLE the Student should always TCCOrd 

 COAT OF THE HUMAN INTESTINE. X 560. , ., . . . , , ,. , 



whether it is circular, longitudinal, 



or oblique in relation to the organ of which it forms a part. This relation 

 is independent of the plane in which the organ has been sectioned, and in 

 many small sections it cannot be determined from observation. He should 

 add the way in which the fibers are cut, whether lengthwise or across, and 

 this depends entirely on the way in which the sections happened to be made. 

 It can always be observed in the specimen. Thus in Fig. 88 the student 

 should observe an inner layer of muscle fibers cut lengthwise and an outer 

 layer cut across. If he knows that the inner layer of intestinal muscles 

 is generally circular, and the outer layer is longitudinal, he infers that 

 Fig. 88 is from a cross section of the oesophagus. If the oesophagus had 

 been split, the inner circular fibers would have been cut across and the 

 outer ones cut lengthwise. Being told that Fig. 93 represents the circular 

 layer of muscle, he can state whether it is from a transverse or a longitudinal 

 section of the intestine. 



CARDIAC MUSCLE. 



Cardiac muscle begins as a mesenchyma with very broad protoplasmic 

 connections between its cells. This syncytial condition is retained in the 



