52 ME. SWALE VINCENT ON THE 



genera, as Scyllium, paired in others, as Raja, which lies in the region of the hinder 

 end of the kidney — in the middle line, as a rule, in the first case ; on the inner and 

 hinder border of the kidney in the second (PI. IX. figs. 1, 2, 3, & 4, PL X. figs. 5, 6, 

 & 7, is.). This structure was called by Balfour the " interrenal " body, and has since 

 usually borne this name. The other set of structures is a segrnentally arranged series 

 of paired bodies, placed on the intercostal or parietal branches of the aorta, and 

 extending in many cases throughout the whole length of the abdominal cavity (PL IX. 

 figs. 1-4 ; PL X. figs. 5, 6, & 7, ax.L, & s.r.). 



a. Selachoiuei and Batoidei. 



I have examined the following seven species, and in some cases several individuals of 

 the same species : — 



Scyllium canicula. Raja batls. 



„ catulus. ,, clavata. 



Acanthias vulgaris. „ maculata. 



Rhina squatina. 



The Segment-ally arranged Bodies. — These are disposed in much the same manner in 

 all Plagiostomes. Their general arrangement has been already well described by 

 Leydig, Semper, and Balfour; and Chevrel has given a description of their anatomical 

 connections with the sympathetic. It is therefore only necessary for me to give a 

 brief account of their usual anatomy, emphasizing such points as may seem to need it. 



These bodies are placed for the most part in a very definitely segmental manner 

 (PL IX. fig. 2). The anterior pair are always elongated and equal in size to several of 

 the following bodies (Pis. IX. & X. figs. 1-7, ax.h.) ; as a matter of fact they seem to 

 correspond usually to three or four segments. They are arranged on branches of the 

 aorta, the intercostal arterioles (PL IX. figs. 1 & 4 ; PL X. figs. 5 & 6), and extend on 

 each side of the vertebral column from the front part of the sinus of Monro to a variable 

 distance posterior to the origin of the posterior cardinal veins. The anterior pair and 

 some of those bodies which immediately follow these on either side are placed in the 

 cavity of the sinus, and therefore during life are bathed in its blood (Pis. IX. & X. 

 figs. 1-7, ax. h., s.r.). They usually more or less completely surround the artery with 

 their substance, and with the aid of a lens one can nearly always see the artery, vein, 

 and a fine nerve distributed to each segmental body. The first pair are placed on or 

 near the axillary arteries, hence their old name "Axillary Hearts." An arteriole usually 

 communicates between the axillary and the succeeding branch of the aorta, and runs 

 through the whole length of the body (PL IX. figs. 2 a & 4). 



In the anterior part of the abdominal cavity these bodies have no relation to the 

 kidney-substance, but in the region of this organ they become more or less imbedded 

 in it. Where the renal substance is distinctly segmented they are often placed deep 

 down in the grooves which separate the segmental portions, and are often in this way 

 almost completely hidden. They usually overlap the region of the interrenal, and often 



