FIBRES OF THE HEART. 



627 



circle it arrives again at the anterior edge of 

 the septum, receives another fasciculus of fibres 

 from the aorta, and is marked CPCAA. It 

 is then seen to take its course round the base 

 and in front of the right ventricle. As it passes 

 by the right aspect of the aorta, it again receives 

 from it a fasciculus of fibres, and is lettered 

 CPCAA A ; on reaching the posterior edge 

 of the septum, it is further augmented by two 

 accessions of fibres, one from the aorta at its 

 posterior aspect, and the other from the middle 

 layer of the septum. This combination of 

 fibres from various sources is indicated by the 

 combination of their initial letters, CPCAAAAC. 

 It should be borne in mind that C large 

 is the synalepha of CRC the initials of the 

 primitive mass of blended fibres. This band, 

 in passing along the base of the left ventricle, 

 makes at first a gentle twist of its fibres form- 

 ing the brim of this chamber; it afterwards 

 makes a sharp twist and assumes the form of a 

 rope, by which means its fibres are transferred 

 to the interior of the ventricle. In descending 

 this chamber, they expand again into a layer, 

 and wind spirally round its cavity, first forming 

 the internal layer, R, of the septum, and then 

 associating with the expanded fibres of the two 

 carneae columnae, and thus arrive at the points 

 from which we commenced tracing them. We 

 now return to the anterior edge of the septum, 

 S, in order to trace the shorter band. At this 

 part the primitive mass of blended fibres splits 

 into two bands : the longer passes behind the 

 right ventricle through the septum as already 

 described ; the shorter passes in front. The 

 shorter first receives a considerable accession 

 of fibres from the right surface of the septum, 

 which pass down from the aorta, and from the 

 two carneae columnae springing from this sur- 

 face : it is lettered CACC ; it describes one 

 spiral circle round both ventricles. It first 

 passes over the lower half of the right ventri- 

 cle, forming the apicial band of the middle 

 layer of its proper wall, and then round the 

 left ventricle in an oblique direction to the base, 

 and terminates at the aorta near the anterior 

 coronary track, having completed its spiral 

 circle round the heart. 



As the demonstration has, in reference to the 

 construction of the septum and of the right 

 ventricle, been unavoidably disconnected, it is 

 requisite to give a more systematic and com- 

 prehensive description of their particular for- 

 mation. 



The septum is composed of three layers : a 

 left, a middle, and a right layer. The two 

 former properly belong to the left ventricle ; 

 and the last or right layer exclusively pertains 

 to the right ventricle. The two former are 

 composed of the primitive mass of fibres de- 

 rived from the rope and the carneae columnae of 

 the left ventricle ; the left layer being formed 

 of the expanded fibres, R, of the rope, RRj^rg^SO, 

 in their first sweep round the cavity ; and the 

 middle layer of the continued fibres of the 

 rope in its second sweep, blended with the ex- 

 panded fibres of the two carneae columnae. 

 These blended fibres form the extended layer 

 CRC ; its cut edge a applies itself to the cut 



edge b, evidently forming the middle layer of 

 the septum. The last or right layer of the 

 septum has not the same origins as the two 

 former have. Its fibres arise from the root 

 and lower margin of the valve of that section 

 of the aorta which pertains to the right ven- 

 tricle, from that part of the root of the pulmo- 

 nary artery contiguous to the aorta, and from 

 the carneae columnae of the right surface of the 

 septum. The fibres attached to the aorta and 

 pulmonary artery may be seen in Jig. 278, lettered 

 A and R respectively, and infg. 280 the fibres 

 from the aorta blended with those of the car- 

 neae columnae are exhibited marked ACC, 

 forming the right layer of the septum. 



The rig/it ventricle. Although the right layer 

 of the septum belongs anatomically to the right 

 ventricle, yet when functionally considered it 

 pertains, as well as the other layers, entirely to 

 the left. For the concavity of this layer is, 

 like that of the other layers of the septum, to- 

 wards the cavity of the left ventricle, and 

 therefore during the systole approaches the axis 

 of this cavity, while it recedes from that of the 

 right ventricle ; thereby assisting in the propul- 

 sion of the blood from the former, and to a 

 limited extent counteracting the propulsive effort 

 of the latter ventricle. 



The right ventricle has, therefore, but one 

 proper wall, which is connected to the left 

 ventricle in a manner to be described hereafter. 

 The right chamber should be divided into three 

 channels : the auricular, the pulmonary or 

 ventricular, and the apicial. The auricular is 

 that which receives the blood directly from the 

 right auricle ; the pulmonary is that formed 

 by the fibres which arise from the root of the 

 pulmonary artery at its entire circumference : 

 in Jig. 278, the pulmonary artery, PP, and the 

 fibres, P, are seen turned a little upon their 

 axis, by which means the fibres are rendered 

 oblique, and the channel the more complete ; 

 and the apicial channel is that which forms the 

 channel of communication between the other 

 two, and which extends to the apex. The pro- 

 per wall is considered as having three layers, 

 the superficial, middle, and internal, although 

 they cannot always be detached from each 

 other. The superficial is composed of the 

 mere superficial fibres of this wall, having the 

 same origins and terminations as have its sub- 

 jacent fibres; it forms the left wing CACC of 

 Jig. 279. and may be seen in fg. 281, raised 

 from the right ventricle and reflected over the 

 base marked CACC. The middle layer is 

 composed of two bands, the apicial and the 

 basial. The apicial is formed of the first semi- 

 circular portion of the shorter band of the 

 heart, and passes over the lower half or apicial 

 channel of this chamber ; it lies separated and 

 extended over the apex of Jig. 281, marked 

 CACC. The basial band of this layer is 

 formed of the first semicircular portion of the 

 longer band as it makes its second circle round 

 the heart. It is bisected and separated as 

 seen at CPCAA, of Jig. 281; in its natural 

 situation it passes over the pulmonary and 

 auricular channels of this ventricle, and is 

 closely connected to the base. The internal 



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