182 OEIOINAL ARTICLES. 



it, allows passage to a large nerve for the depressors of the fin, by 

 the space between it and the " nlna." (I merely make this obser- 

 vation without endeavouring to draw any morphological conclusion.) 

 The " clavicle " is very remarkable. It articulates mth the coracoid 

 and scapula, and passes downwards and backwards in continuation 

 of the direction of the latter to a point a little beyond the carpal 

 range. There it terminates in a joint, and sends back a barb-like 

 process which lies outside the two last carpal bones, so as completely 

 to fix that range in the plane from before backwards. 



The pectoral fin has twelve rays, which are based on cartilages, 

 on the same principle as the other fins. It is worked by four 

 muscles, two of whicli, arising one from the external, the other from 

 the internal surface of the " ulna," respectively depress and elevate 

 it ; while the other two, arising, one from the lower part of the 

 coracoid, to be inserted along with the tendons of the depressor, 

 the other from the upper part of the coracoid, to be inserted with 

 the tendons of the extensor, more especially serve to rotate it. 



A]S"ATOMT OP THE ViSCEEA. 



The Abdominal cavity. — There is a general peritoneal cavity. Tlie 

 intestines are coiled closely together, and the coiled mass is sur- 

 rounded by one tight in\'estment of peritoneum with an appearance 

 of muscular fibres in its substance. The general arrangement of the 

 peritoneum is very simple. A mesenteric fold arises along the 

 whole length of the superior and posterior margins of the abdominal 

 cavity, beginning in front where the oesophagus enters the abdomen, 

 and suspending it and the stomach by their dorsal margin from the 

 superior wall, and the coil of intestines from the posterior. The 

 right and left layer of peritoneum, after iuA'csting the stomach, meet 

 beneath it, and pass down to the liver and invest it, and again 

 beneath the liver a fold of peritoneum surrounds the vessels which 

 pass between it and the intestines. The intestinal coil is in addition 

 connected with the right edge of the liver by a special short stout 

 ligament of peritoneum. (Pt. VI. fig. 2, /!) A distinct and free 

 funnel of pex'itoneum surrounds the vessels entering the cardiac 

 cavity from the li^'er. 



The liver occupies about half the bulk of the abdomen. It con- 

 sists principally of left lobe ; but in front it passes imder the stomach, 

 and slightly to its right side, so as to form a small right lobe. From 

 the two lobes, two hepatic veins pass directly from the liver into the 

 auricle of the heart : they enter side by side, with about an inch 

 between them, and the left is three or four times the diameter of the 

 right. There is a large gall bladder with a long gall duct which 

 opens into the cavity of the stomach itself (Ft. V. fig. 2.) The 

 spleen is small and compact ; it lies between the liver and stomach. 



Tlie stomach and intestines have very strong muscular walls like 

 a turtle's, in compensation for the absence of muscular abdominal 



