494 LECTURE XX. 



presents the same uniform thickness as that of the stomach. The 

 muco-epithelial lining membi'anes are disposed in very delicate 

 transverse plaits. In Orbicida the intestinal canal is somewhat 

 longer, bends to the right side, where the vent opens into the pallial 

 cavity near the right anterior adductor. In Lingula the intestine 

 is still longer, forms two bends before it extends forwards to ter- 

 minate at the right side, in the pallial cavity. 



The liver {q) is about three times the bulk of the stomach, and 

 forms the most conspicuous of the chylopoietic viscera, when the 

 abdominal cavity is exposed. It consists of very numerous ramified 

 follicles, the terminal ones of which are of equal dze, and their round 

 closed ends give the apparently granular exterior surface to the 

 gland: the intimate structure of the hepatic follicles , in Ter.Jiaves- 

 cens agrees with that described in my earlier Memoir*, in Ter. 

 ■psittacea and Ter. cliilensis. There is no natural division into lobes ; 

 a slight pressure suffices to displace groups of follicles, which then 

 assume the lobular character. The ducts form the common stems of 

 the manifold ramifications, and they are usually two in number, com- 

 municating, each by a distinct aperture, with the cardiac end of the 

 stomach. 



The vascular system of the Brachiopods is peculiarly well adapted 

 to demonstrate that remarkable condition of the veins in the Mollus- 

 cous class which, when first and somewhat imperfectly observed, gave 

 rise to the idea of the blood being extravasated into the lacunae of the 

 viscera and the interstices of other soft parts and tissues. 



Such is the condition of the major part of the vascular system in 

 the TerebratidfE. The hearts are two in number, and distinct ; they 

 consist, as in other Brachiopods, each of an auricle f and a ventricle, 



* CCCI. 



f This organ was first described in my Lectures of 1843 (Lecture XX., deli- 

 vered May 11., published June (No. IX.) of that year), as " a small transversely 

 plicated membranous process, continued from each side of the beginning of the 

 intestine." In the same year, 1843, M. Vogt communicated a memoir on the 

 Anatomy of the Lingula anatina to the " Allgemeinen Schweizerischen Gesell- 

 schaft," at Neuchatel, in -which he described the homologous part as follows: — 

 " Upon each heart lies a peculiar sac, unseen by Cuvier and Owen, but plainly 

 visible in my specimens. This sac lies with its under concave smooth border 

 upon the upper convex surface of the heart, and its free upper border is folded 

 like a shirt-frill. The sac is depressed and hollow : at the connecting line of the 

 folds, where this rises teat -wise (zitzenartig), there is a fissure, which leads to an 

 extremely delicate canal, whose further continuations I could not follow; but 

 it seemed to me that it opened externally between the two lobes of the mantle," 

 p. 12. 



No other relation of this sac to the heart is recognized, save its contiguity or 

 contact with that organ : respecting the heart itself, M. Vogt repeats the descrip- 

 tion by Cuvier, viz. that there are two, and he expressly states that they are 



