62 GENERAL ANATOMICAL CHARACTERS 



The essentially bipartite character of the organ and its uniformity 

 of construction throughout the class are thus not lost sight of, even 

 in the most complex forms. The left segment of the liver is rarely 

 complicated to any further extent, except in some cases by minor 

 or secondary fissures marking off small lobules, generally inconstant 

 and irregular, and never worthy of any special designation. On 

 the other hand, the right segment is usually more complex. The 

 gall-bladder, when present, is always attached to the under surface 

 of the right central lobe, sometimes merely applied to it, in other 

 cases deeply embedded in its substance. In many instances the 

 fossa in which it is sunk is continued to the free margin of the 

 liver as an indent, or even a tolerably deep fissure (cf). The 

 portal fissure (p), through which the portal vein and hepatic artery 

 enter and the bile-duct emerges from the liver, crosses the right 

 central lobe transversely, near the attached border of the liver. 

 The right lateral lobe always has the great vena cava (vc) either 

 grooving its surface or tunnelling through its substance near the 

 inner or left end of its attached border ; and a prolongation of this 

 lobe to the left, between the vein and the portal fissure, sometimes 

 forming a mere flat track of hepatic substance, but more often 

 a prominent tongue-shaped process, is the so-called "Spigelian lobe" 

 (s). From the under surface of the right lateral lobe a portion is 

 generally partially detached by a fissure, and called the " caudate 

 lobe" (c). In Man this lobe is almost obsolete, but in most 

 mammals it is of considerable magnitude, and has very 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 

 through 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. 



Considerations derived from the comparatively small and simple 

 condition of the liver of the Ungulata, compared with its large 

 size and complex form in the Carnivora, have led to the perhaps 

 too hasty generalisation that the first type is related to a herbivorous 

 and the latter to a carnivorous diet. The exceptions to such a 

 proposition are very numerous. The fact of the great difference 

 between the liver of the Cetacea and that of the Seals cannot 

 be accounted for by difference of habits of life, though it perhaps 

 may be by difference of origin. 1 



1 For further details of these modifications, see Flower's ' ' Lectures on the 

 Comparative Anatomy of the Organs of Digestion of the Mammalia," Medical 

 Times and Gazette, Feb. -Dec. 1872. 



