ANATOMY OF THE SPLEEN. 473 



reasonable of the many theories that have been entertained concerning their office in 

 the economy. Under this idea, these organs have been called blood-glands or vascular 

 glands; but, inasmuch as the supposition that these parts effect changes in the blood 

 or lymph is merely to supply the want of any definite idea of their function and rests 

 mainly upon analogy with certain of the functions of the liver, we shall retain the name 

 ductless glands, as indicating the most striking of their anatomical peculiarities. 



As far as presenting any definite and important physiological information is concerned, 

 we might terminate here the history of the ductless glands. It is true that the largest 

 of them, the spleen, was extensively experimented upon by the earlier physiologists; 

 but, in point of fact, investigations have done little more than exhibit a want of knowl- 

 edge of the functions of these remarkable organs; and the literature of the subject is 

 mainly a collection of speculations and fruitless experiments. There are, however, some 

 interesting experimental facts with relation to the spleen and the suprarenal capsules, 

 although they are not very instructive, except that they indicate the extremely narrow 

 limits of our positive knowledge. These few facts, with a sketch of the anatomy of the 

 parts, will embrace all that we shall have to say concerning the ductless glands. Under 

 this head are classed, the spleen, the suprarenal capsules, the thyroid gland, the thymus, 

 and sometimes the pituitary body and the pineal gland. These parts have certain 

 anatomical points in common with each other, but, on account of our want of knowl- 

 edge of their functions, it is difficult to distinguish, as we have done in other organs, 

 their physiological anatomy. 



Anatomy of the Spleen. 



The spleen is situated in the left hypochondriac region, next the cardiac extremity of 

 the stomach. Its color is of a dark bluish-red, and its consistence is rather soft and fri- 

 able. It is shaped somewhat like the tongue of a dog, presenting above, a rather thick- 

 ened extremity, which is in relation with the diaphragm, and below, a pointed extremity, 

 in relation with the transverse colon. Its external surface is convex, and its internal 

 surface, concave, presenting a vertical fissure, the hilum, which gives passage to the ves- 

 sels and nerves. It is connected with the stomach by the gastro-splenic omentum and is 

 still farther fixed by a fold of the peritoneum passing to the diaphragm. It is about five 

 inches in length, three or four inches in breadth, and a little more than an inch in thick- 

 ness. Its weight is between six and seven ounces. In the adult it attains its maximum 

 of development, and it diminishes slightly in size and weight in old age. In early life it 

 bears about the same relation to the weight of the body as in the adult. 



The external coat of the spleen is the peritoneum, which is very closely adherent to 

 the subjacent fibrous structure. The proper coat is dense and resisting; but, in the 

 human subjept, it is quite thin and somewhat translucent. It is composed of inelastic 

 fibrous tissue, mixed with numerous small fibres of elastic tissue and a few unstriped mus- 

 cular fibres. 



At the hilum, the fibrous coat penetrates the substance of the spleen in the form of 

 sheaths for the vessels and nerves ; an arrangement analogous to the fibrous sheath of 

 the analogous structures in the liver. Th,e number of the sheaths in the spleen is equal 

 to the number of arteries that penetrate the organ. This membrane is sometimes called 

 the capsule of Malpighi. The fibrous sheaths are closely adherent to the surrounding 

 substance, but they are united to the vessels by a loose fibrous net-work. They follow 

 the vessels in their ramifications to the smallest branches and are lost in the spleen-pulp. 

 Between the sheath and the outer coat, are numerous bands, or trabeculre, presenting the 

 same structure as the fibrous coat. The presence of elastic fibres in these structures can 

 be easily demonstrated, and this kind of tissue is very abundant in the herbivora. In 

 the carnivora the muscular tissue is particularly abundant and can be readily demon- 

 strated; but in man this is not so easy, and the fibres are less numerous, some anatomists 

 denying the existence of any muscular structure. These peculiarities in the fibrous struct- 



