Strnetnre of Liimiliis IToart ^rnsole. 411 



A few more points may be of interest. The trabeculse take their 

 origin from the basement membrane. Here, and in the connective 

 tissue guarding the ostia are the only places where fibers have been 

 found to end. The ending is not often conical, as noticed in skeletal 

 muscle. The fibers rather fray out and the connective tissue inserts 

 itself between the fibrils. The connection is thus one of fibrils to 

 connective tissue rather than that of an entire strand. 



The trabeculse are often separated by narrow clefts into which the 

 connective tissue sheath inserts itself, as may be seen in Eig. 9. 

 This makes the trabecula;? on the average rather narrow in diameter. 

 The function of the sheath in Fig. 9 may be a support, since the 

 cross striation shows that the fibrils are not in synchrony. 



Bands of Eberth are of course not found in the Limulus heart. 

 These structures do not appear in man until after birth and are not 

 found lower in the animal kingdom than in the birds. Their 

 absence in Limulus is therefore of no significance. 



Summary. 



The heart musculature of Limulus is a double syncytium. It 

 consists of branching, anastomosing trabt^cula? individualized by con- 

 nective tissue sheaths, within which heart fi\)cv^ l)raneli and anasto- 

 mose, thus forming a continuous network of contractile tissue. 



The heart tissue studied agrees with all heart tissue in these funda- 

 mental facts. 



1. It has the regular cross striation. 



2. Contractile fibrils are continuous throughout the musculature, 

 ending only where the fibers take their origin. 



3. The trabeculse are provided with a peripheral covering which 

 may serve as a dialyzing membrane. 



4. The heart muscle is a syncytium. 



The fact that the heart musculature is- syncytic would show that 

 a continuity of musculature is not decisive evidence for the myogenic 

 theorv of conduction. 



