NORMAL ANATOMY OF THE LIVER. 



175 



of the organ is, however, more apparent than 

 real, for the numerous cells may be considered 

 as so many follicles from which smaller fol- 

 licles are developed. The cellular character of 

 the organ depends upon the more extensive 

 subdivision of the follicles, their assemblage 

 in greater numbers, their consequent compres- 

 sion, and the adhesion of their parietes. In 

 the Sepia family the spongy structure of the 

 hepatic organ is still more distinct. It is chan- 

 nelled into numerous canals, from which smaller 

 canals branch off in various directions; from 

 these branches cells are developed, and the 

 parietes of the cells are every where surrounded 

 by smaller and smaller cells, the entire texture 

 being very similar in arrangement to the cel- 

 lular lung of the higher reptilia. 



The liver in Vertebrata is more close and 

 complex in its structure and less amenable to 

 the observations of the anatomist than in the 

 inferior series. We observe nothing, even in 

 the lowest fishes, which bears any direct com- 

 parison with the cellular structure of the liver 

 of Cephalopoda. The general character of the 

 organ in fishes is loose and flabby, shewing 

 that, although difficult to demonstrate, its in- 

 ternal texture evidently contains numerous tu- 

 buli. If the efferent duct of the liver of a 

 fish be inflated, the whole organ appears dis- 

 tended ; hence we might infer that the primi- 

 tive structure of the organ is precisely the 

 same, consisting in the ramifications of the 

 hepatic tubuli or ducts, the increased wants 

 and higher position of the animal demanding 

 an augmented extension of surface. This is 

 the great principle in the development of all 

 glandular organs extension of surface. The 

 simple follicle is sufficient for an animal so low 

 in the scale as a cavitary entozoon, but as the 

 functions of the animal increase, its simple fol- 

 licle must be extended to a greater length, or 

 branched or ramified ; and as high in the ani- 

 mal scale as the Vertebrata these subdivisions 

 have attained so great a degree of minuteness 

 that they are demonstrable to the practised eye 

 only through the aid of the highest microscopic 

 powers. 



Miiller arranges the glandular system into 

 simple and compound glands. The former he 

 divides into two groups : 1 . " simplest glands" 

 which " are mere recesses of greater or less 

 dimension in the surface of a membrane;" and 

 2. " more complicated forms," in which se- 

 veral of the recesses are assembled together 

 and open by so many distinct mouths, or they 

 unite and form a common duct which termi- 

 nates by a single opening. The " compound 

 glands" he likewise subdivides into two groups: 

 1. those which " ramify with a certain degree 

 of regularity, the principal trunk giving off 

 branches laterally at certain intervals, these 

 sending out in the same way side branches, 

 which in their turn afford a third set." This 

 disposition constitutes lobulated glands, and is 

 the type of conformation of the liver in Inver- 

 tebrata. 2. " The second group of the glands 

 with ramified secreting tubes consists of those 

 in which the ramification is irregular, and in 

 which there is no division and subdivision of 



the gland into" secreting " lobules. The liver 

 of Mammalia belongs to this group." 



The form of the liver in Fishes corresponds 

 with the direction of the long axis of the body ; 

 thus, for instance, it is elongated, and con- 

 sists of a single lobe in the eel, while in the 

 skate it is broad and extends into each lateral 

 half of the abdominal cavity. In other fishes 

 it is variously divided into lobes, and is often 

 placed altogether on the left side of the body. 

 In the class Amphibia, the liver also corresponds 

 with the form of the body of the animal: in the 

 frog it is short and divided into two primary lobes 

 and several lobules ; in the lengthened forms it 

 is long and less divided. In the class Reptilia 

 the liver is large, and bears an equal relation to 

 the form of the visceral cavity. It is long and 

 undivided in Ophidia, and short and divided 

 into a right and a left lobe in Sauria and Che- 

 Ionia, the two lobes being spread out over the 

 intestines. In Birds there is great uniformity 

 in the form and size of the liver. It is smaller 

 in proportion to the bulk of the body than in 

 Reptilia and Fishes, and larger than in Mam- 

 malia. It is situated in the middle line of the 

 visceral cavity, and receives the heart into a 

 depression upon its under surface. In the 

 class Mammalia the liver is very much reduced 

 in size, and is more compact and firm than in 

 the lower vertebrata. In animals with simple 

 stomachs it is situated in the middle line of the 

 abdomen. In others, with large or compound 

 stomachs, it is pressed towards the right side. 

 The number of lobes does not depend upon a 

 greater or less division of the liver into parts 

 in accordance with the activity and mobility of 

 the animal, but obeys a law in the animal 

 economy, by which new parts are superadded 

 in proportion to the increase of the wants of 

 the creature. Man is placed at the foot of the 

 scale in the progressive complication in exter- 

 nal form of the liver of vertebrata ; the entire 

 organ may be considered in him as a central 

 lobe, the lobus Spigelii being the rudiment of 

 a second or right lobe. The liver of the ourang 

 offers the same character. Ruminants have 

 also a liver which presents the most rudimen- 

 tary form of division. The liver of man is the 

 type of the central or principal lobe, to which 

 are added upon each side, in the animal scale, 

 a right and a left lobe, and from these latter 

 are developed a right lobule and a left lobule. 

 This most complicated form of liver, consisting 

 of five lobes, is met with among Carnivora and 

 Rodentia; and throughout Mammalia, the suc- 

 cessive additions and subtractions from this 

 normal type form a constant and generic cha- 

 racter. Besides this real division of the liver 

 into five lobes, fissures of various depth are 

 constantly met with, as in man, which give 

 the appearance of a much greater subdivision. 

 These secondary portions are to be looked upon 

 as the mere results of separation, and have no 

 relation with the primitive type. A most ex- 

 traordinary form of liver is met with in a small 

 rodent animal from Cuba, the Capromys, in 

 which the whole surface is divided by deep 

 fissures into small masses of a triangular and 

 quadrangular form, like the kidney of a bear. 



