198 PATTEN AND REDENBAUGH. 



gives a branch to the lateral sympathetic nerve {l.s.n.), and then continues through 

 the pericardium to the areolar tissue and epidermis haemal to the heart. After 

 giving off numerous branches to the epidermis, it dips down in the median line to 

 the median cardiac nerve {m.c.n.). 



Fig. 7. A cross-section of one corner of the heart of a young Limulus (mag- 

 nified 100 times). 



It shows the three layers of the heart ; the layer of longitudinal connective- 

 tissue fibers {/.c.s.) is seen in cross-section upon the outside of the hyaline base- 

 ment membrane {b.mem.), and the layer of muscle fibers {a.m.f.) is seen upon the 

 inside. These are cross-striated and anastomose freely. Their bases are expanded 

 where they are attached to the basement membrane. 



Fig. 8. Heart of a young Limulus (5 in. long). It has been slit open along 

 the neural side, spread out and viewed from the interior (magnified 10 times). 



The specimen, from which the drawing was made, was treated by Lowits's gold 

 chloride method, which macerated off the muscles, leaving the nerve plexus intact. 



The eight pairs of ostia {os.'''^^) are indicated, and also the rudimentary ostia 

 {r.os.) anterior to the aortic valve (a.v.). The two aortic arches {ao.a.) are slit 

 open. The frontal artery, with its opening in front of the aortic valve, is seen 

 between the aortic arches. 



The lateral arteries (l.ar.^''^) emptying into the collateral artery {car.) and the 

 superior intestinal branches and superior abdominal artery (s.a.ar.) are also repre- 

 sented. The anterior lateral artery {/.ar.^) is cut open to show the two semi-lunar 

 valves (s.v.^). 



The median cardiac nerve (rn.c.n.), with its blackened masses of ganglion cells, 

 gives off branches opposite each pair of ostia to the plexus of nerves which com- 

 municates with the lateral cardiac nerves {l.c.n.). 



