210 DR. T. DAVIDSON OX RECENT BRACHIOPODA. 



and, having their edges attached to the valves, give a definite form to the enclosed 

 space, which is -wide, rounded in front, and tapering backwards. 



" On turning hack the ventral pallial lobe the arms are observed occupying the greater 

 portion of the pallial chamber, which is about half the length of the shell. The mouth 

 is situated, as in the Terebratulidaj, in the brachial groove ; and on each side of it, a 

 little below, are the ovarian outlets, which penetrate the anterior wall of the body. On 

 the right side of the animal, l)etween the margins of the mantle, is placed the anal orifice, 

 which is A-ery distinct and easily detected. 



" On removing the dorsal parietes in Liiigula, the alimentary tube is found to occupy 

 a central position as in the articulated tribes, the anterior portion being buried, as in 

 them, beneath the lobulated liver, which is rather bulky. On displacing the latter, the 

 heart is seen attached to the upper surface of the stomach, and the two dorsal genital 

 organs are entirely exposed, extending nearly the whole length of the perivisceral 

 chamber. At the sides and in front of these are the extremities of the muscles, and 

 behind are the convolutions of the intestine." 



Elaborate descriptions of the various muscles and of their functions have been published 

 by Cuvier, Owen, Vogt, Hancock, Gratiolet, Semper, Woodward, Morse, Brooks, Beyer, and 

 others, each anatomist giving difl^crent names to the different muscles and interpreting 

 their functions differently. Much confusion consequently ensued. In 1873 Prof. W. 

 King devoted much time and care to an examination of the muscular system in Lingula 

 anatina * ; and as I had occasion to confirm his observations by personal investigations, 

 I cannot do better than reproduce some of the details given in his valuable memoir. 



In the interior of both valves the muscvilar and visceral area forms a large lozenge- 

 shaped space, which, commencing close to the beak, extends to about two thirds of the 

 length of the shell and tapers most anteriorly, and is most elevated along the middle ; 

 this area constitutes tlie thickest part of the shell, where the calcareous element prevails, 

 and its colour is whitish, contrasting with the greenish horny aspect of the remainder 

 of the interior. This is also the most important compartment of the posterior half of 

 the shell-cavity, and is bounded by a highly muscular wall or parietal baud, b (fig. 22, 

 A, B), and contains the viscera and muscles. King proposes to name this division 

 the splanchnocosle, or visceral cavity, and adds : — "The anterior half of the pallial inter- 

 space is open all round (sides and front) except at its back, which is formed by the 

 anterior parietal. It encloses the arms or brachial appendages, and may therefore be 

 called the brachiocoele or brachial chamber. Its upper and under surfaces (dorsal and 

 ventral lobes of the pallium or mantle) are highly vascular. 



"The sides of the splanchnoccele in its posterior half, as just stated, are rather strongly 



incurved, giving rise to two lateral spaces I propose to give the name plenrocoeles 



to these spaces, simply from their position as side chambers." The area within the 

 parietal, b, is occupied by the liver, genitalia, and shell-muscles. "There are five 

 pairs, and an odd one. Three pairs, Avoodcut, fig. 22, A, B {j, k, I), are lateral, having 

 their members limited to the sides of the shell. One pair is traiismecUcm (i), each 



* Ann. & Mag. Nat. Hist, -ithser. vol. xii., 1873. 



