THE HEART. 



217 



by reference to Fig*. 137. A layer of circular fibres {C31) extends 

 round the whole ventricle, and from it more or less radial or trans- 



I 



CM 



ï'ig- 137- 



TM 



CAT 





Tflr 



7.AI 



LM 





'LM 



I. Transverse section through the junction of the hinder and middle thirds of the ventricle of R. Icm- 

 poraria. II. Transverse section through junction of middle and anterior thirds of the same heart. 

 Dec. I, Syst. I, Leitz. The heart was freely distended i with dilute spirit, and so hardened. — G. H. 



. CC Central cavity. 



CM Circular muscle. 



LM Longitudinal muscle. 



TM Transverse muscle. 



verse bands [TM, also Fig-. 138 T2I) pass inwards ; these, in the apical 

 portion of the ventricle, seem to extend almost transversely across ; 

 towards the base they are directed onwards and forwards towards 

 the auricles. Of these bands some, near the apex, can be traced 

 directly to the opposite side, others join the wall more anteriorly, 

 and still others join bands of muscular fibres {LM), which may be 

 described as longitudinal, and form the Mnsculi iiapillareii. In the 

 anterior portion of the ventricle the same arrangement holds good, 

 but is modified to form a central cavity; still more anteriorly, 

 at the junction of auricles and ventricle, the trabecular structure is 

 much less apparent, the fibres being closer and mainly circular. 



In the auricles the muscular fibres are chiefly arrang-ed in circular- 

 rings which cross one another; on the inner surface, however, 

 traces of an arrangement similar to that in the ventricle may be 

 made out. In the heart, from which the sections in Fig-. 137 



1 The base of the ventricle measured, when distended, 8 mm. by 5 mm. 



