TRANSACTIONS OF THE SECTIONS. 151 



fissure. The riglit central lobe, therefore, on its under surface does not reach to 

 the attached border of the liver, but is alwaj's bounded in that direction by the 

 portal fissure. Moreover, the gall-bladder when present is always in relation to 

 its under surface. The position of this receptacle with respect to the lobe may 

 var}'; sometimes it is merely applied to its surface, loosely connected by con- 

 nective tissue ; in other cases it is deeply imbedded in a fossa. Very often it is 

 filaced near the middle of the lobe ; sometimes close to one or the other of its 

 atoral boundaries. In many cases the fossa in which the gall-bladder is sunk is 

 continued to the free margin of the liver as an indent, or even a tolerably deep 

 fissure. This is called the cystic fissure ; but, in consequence of its irregularity 

 of position and frequent absence, it is not of the same importance as the other 

 fissures which have been named, and does not mark off any distinct divisions of 

 hepatic substance. 



The right lateral lobe always has the great vena cava either grooving its surface 

 or tunnelling through its substance near the inner or left end of its attached border; 

 and a prolongation to the left, between the vein and the portal fissure, has long 

 been known under the name of the Spif/elian lobe. This is always a distinct 

 licpatic region, sometimes a mere narrow fiat track, but more often a prominent 

 tongue-shaped process. Whatever may be its form, it is bounded in front, or 

 towards the free surface of the liver, by the portal fissure ; on the left by the 

 iissure of the ductus venosus (unless the vessel is bridged over by hepatic sub- 

 stance) ; posteriorly and partially on the right by the vena cava, but between this 

 vessel and the right end of the portal fissure it is continued onwards into the ad- 

 joining part of the right lateral lobe. 



The main body of the right lateral lobe is most commonly divided into two 

 parts, not by a cleft, such as the lateral fissures, passing from the upper to the 

 lower surface of the liver, but by one which severs a part off from the under 

 surface. This is the caudate lobe ; and the fissure which separates it from tJie right 

 lateral lobe may be called the " fissure of the caudate lobe." In man it is almost 

 obsolete ; but in most mammals it is of very considerable magnitude, and has verv 

 constant and characteristic relations. It is connected by an isthmus at the left 

 (narrowest or attached end) to the Spigelian lobe, behind which isthmus the vena 

 cava is always in relation to it, channelling tiirough or grooving its surface. It 

 generally has a pointed apex, and is deeply hollowed to receive the right kidney, 

 to the upper and inner side of which it is applied *. 



On Pahe-Bate and the Forces tvJiich vary it. By A. H. Gahrod. 



Tlio number of the heart's beats can be proved to depend on variations in the 

 resistance ofiered to the flow of blood through the small arteries, and not at all on 

 the blood-pressure. Poiseuillc showed that the flow of fluids through capillary 

 tubes varies directly as the pressure. From these facts it can be proved that to 

 maintain a uniform circulation, such as the systemic, it is essential that the capa- 

 city of the arterial system, including the heart, must vary directly as the blood- 

 pressure ; and therefore it is necessary that the heart always recommences to beat 

 when the tension or pressure of the blood has fallen a certain invariable proportion, 

 and then only. The known variations in pulse-frequency in health are all 

 explicable on this supposition, for they can be proved to be caused by modifications 

 in the arterial peripheral resistance ; thus while standing the body-wei<>-ht is 

 supported by rigid tissues, but while lying soft parts are compressed, and therefore 

 resistance is introduced. The next point considered is the cardiograph law of the 

 author ; and an explanation is given of its significance, which leads to the results 

 that the nutrition of the heart varies directly as the blood-pressure and as the 

 square root of the time of nutrition. Eeasons are also given to show that the 

 cardiac revolution must be divided into three instead of two parts, — first, systole : 

 next, diaspasis, or the valve closure interval ; and, lastly, the diastole, 



^ For a figure explanatory of the above paper, see ' ITature,' Aug. 20th, 1872. 



