STRUCTURE OF THE MATRIX OF SEROUS MEMBRANES. 269 



B. THE MATRIX. 



The stroma of the serous membranes is composed of con- 

 nective and elastic tissue. The former consists of undulating 

 fibres united into fasciculi, which form in general a delicate 

 trellis-work interweaving with each other in various directions, 

 and forming at certain points thicker trabeculse in which the 

 larger bloodvessels and lymphatics, as well as nerve trunks, lie 

 imbedded. The connective tissue is thus arranged in the me- 

 sentery, in the delicate and sparing subserous tissue of the 

 pleura (12), and in the similar tissue covering the abdominal 

 and thoracic surfaces of the centrum tendineum. On the other 

 hand, the layer of connective tissue may present a more tendi- 

 nous appearance, as on the centrum tendineum itself, where in 

 the Rabbit there is on the thoracic surface a circular, and on 

 the abdominal a radially arranged, layer (13), and in part also 

 in the pericardium, in the deeper layers of the pleura intercos- 

 tatis, and in the dura mater. 



A close plexus of very fine elastic fibres runs through this 

 framework of connective tissue, the fibres being for the most 

 part straight or slightly undulating, more rarely strongly 

 looped or spiral. The amount and number of layers of these 

 plexuses of elastic fibres are very variable, being largest in the 

 mesocolon of Mammals and of Man, and in the mesentery of the 

 Guinea-pig, always abundant in the mesentery of the Frog and 

 of Mammals, in the pleura, in the matrix lying superjacent to 

 both the radial and the circular tendinous layer of the centrum 

 tendineum of the diaphragm, and in the pericardium. 



A variable quantity of adipose tissue is found in the mesen- 

 tery and in the pericardium ; in the former it is chiefly found 

 in the larger trabeculse and their subdivisions that run radially 

 from the root of the mesentery towards the intestine, corre- 

 sponding to the course of the larger bloodvessels. Here, as 

 elsewhere in the masses of connective tissue, numerous cellu- 

 lar structures are to be found distributed between the fibres. 

 Such are branched cells with rounded nuclei, forming a close 

 plexus by means of their simple or branched protoplasmic pro- 

 cesses ; various-sized rounded or irregular granulated masses of 

 protoplasm, containing one or several nuclei ; fusiform granular 



