532 ANATOMY OF VERTEBRATES. 



tricle, as Cpca; then describes a second circle round both ventricles, 

 Cpcaa. The band Cacc passing down from the aorta, aa, winds 

 over the lower half of the right ventricle, RV, combines with the 

 apical spirals, whence it can be traced obliquely round the left 

 ventricle to terminate at the aortic circle near the anterior 

 coronary tract. The septum ventriculorum consists of three 

 strata, the left and middle belonging to the left ventricle, the 

 right layer exclusively to the right. 



The contraction of the heart-fibres is called ' systole,' their re- 

 laxation ' diastole.' The parts of the muscular walls of the heart 

 have different degrees of motion : the inner wall or ' septum ' loses 

 length and breadth, but gains in thickness, during the systole : the 

 outer wall changes these dimensions in a greater degree, with 

 changing relative position to the heart's centre : hence it has been 

 termed the ' movable ' wall, and the septum the 6 fixed ' one. The 

 mammillary processes become shorter and thicker cones, and in 

 the degree in which the blood in the ventricles is compressed 

 during * systole,' the valves are held by the tendinous cords 

 attached to their free borders and expanding upon their ventri- 

 cular surface more firmly against eversion, with reflux of blood, 

 into the auricles. The position of the semilunar valves, on the 

 contrary, invites the flow of the blood into the arteries, and forbids 

 return. The ' trabecule ' passing from the ' fixed ' to the ' mov- 

 able ' walls have an analogous function as adding to the resistance 

 of the latter against internal pressure, whence they have been 

 termed c moderator bands.' l 



§ 348. Arteries of Mammalia. — The walls of the arterial tube 

 are so strong as to maintain that form when cut across ; and so 

 elastic as, then, to retract some way within the areolar or con- 

 nective tissue, which surrounds the vessel like a sheath. On the 

 inner surface of the tube amy line formifies 2 as elliptical or irre- 

 gularly polygonal scales, more or less of which show a further 

 stage of condensation, expressed by the term ' nucleate epithelial 

 cell,' fig. 424. The tissue so lined consists of a thin continuous 



proffered indefinitely as the observers arbitrarily select such attachments under the 

 names of ' origins' and ' insertions.' The general conformity of muscular arrangement 

 in the heart of tha sheep is shown in clxxxix", with that previously demonstrated in 

 the human heait, by the author of clxxxvii" and cxxxxvm"; especially in regard to 

 the continuity of certain external with internal fibres. 



1 cxxxxv". p. 123. 



2 I use this term as the correlative of • crystallises,' signifying thereby the tendency 

 in dissolved proteine, amyline, or other albuminoid atoms to assume defined size and 

 shape, under given conditions, both in and out of the living body ; Rainey has shown 

 how such tendency or property effects the superinduction of organic form upon crystal in 

 the formation of shell (ccix") ; and its effects are demonstrated more at large in ecx". 



