ORGANS ANNEXED TO THE ABDOMINAL DIGESTIVE CANAL. 431 



each of these bodies is inclosed. It is probable that, from the blood con- 

 tained in the capillary network, the material is separated which is occa- 

 sionally stored up in their cavity ; the veins being so placed as to carry 

 off, under certain conditions, those contents that are again to be dis- 

 charged into the circulation. Each capsule contains a soft, white, semi-fluid 

 substance, consisting of granular matter, nuclei similar to those found in the 

 pulp, and a few nucleated cells, the composition of which is apparently 

 albuminous. These bodies are very large, after the early periods of diges- 

 tion, in well-fed animals, and especially those fed upon albuminous diet. 

 In starved animals, they disappear altogether.) 



Arteries. These emanate from the splenic artery at different elevations, 

 and plunge into the tissue of the spleen, preserving their reciprocal 

 independence. Their terminal ramifications do not open, as has been 

 said, into venous sinuses, but into minute tufts of capillaries, which traverse 

 the splenic pulp, to be continued by the venous network. 



Veins. All the venous branches of the spleen open into the splenic 

 vein, and are lodged with the corresponding artery in the fissure of the 

 organ. Traced from their commmencement, they are seen to gradually lose 

 their constituent membranes, and to open into sinuses which are only lined 

 by the epithelium of the vessels. It is in these sinuses that the network 

 of venous capillaries which succeed the arterial capillaries, originates. 



Lymphatic vessels. These are found on the external surface of the 

 organ, and along the track of the blood-vessels. (They invest these with 

 a distinct sheath, between which and the parietes of the vessels numerous 

 lymph corpuscles may be found.) 



Nerves. They are derived from the solar plexus, and enveloping the 

 splenic artery, with it enter the spleen. (They appear to be very large, 

 but this appearance is due to the great proportion of ordinary fibrous tissue 

 investing them.) 



From what has been said above respecting the arrangement of the 

 splenic arteries and veins, it will be perceived that the areolas formed by 

 the trabeculse of the fibrous framework contain the pulp, and are not in 

 direct communication with the arterial capillaries. Such an organisation 

 belongs to erectile tissues. The arteries communicate with the veins proper 

 by venous canals channeled in the splenic pulp, and are lined only by ellip- 

 tical cells. These venous canals are extremely dilatable, especially in 

 the Horse. When the splenic vein is inflated, their walls separate and 

 press back the pulp, they become considerably enlarged, and distend 

 the cells of the fibrous structure, but the air does not reach the interior 

 of these cells. 



FUNCTIONS. Nothing precise is known regarding the functions of the 

 spleen ; though they must be of very secondary importance, because animals 

 in which the organ has been extirpated, and which have recovered from the 

 consequences of the operation, have continued to live in apparent good 

 health. Numerous hypotheses have been formed on this subject , two of 

 which, founded on the study of the anatomical peculiarities of the spleen 

 tissue, and on exact physiological observations, are as follows : 1, The spleen 

 is a diverticulum for the portal vein ; 2, The red globules are destroyed in the 

 spleen. 



With regard to the first hypothesis, it is evident that, owing to the 

 presence of the venous sinuses already mentioned, and their great dilata- 

 bility, as well as to the elasticity and contractility of the spleen tissue, the 

 organ is favourably constructed to act as a blood reservoir. M. Goubaux, 



