340 CHORD AT A, 



tympanic cavity. Further back still, on the ventral surface, 

 is a small median longitudinal slit, called \h^ glottis^ leading 

 into the lungs. Lastly, the wide oesophagus leads down to 

 the stomach. 



If the skin be cut open along the mid-ventral line from 

 chin to cloaca it will be noticed that its looseness is due to 

 a large subcutaneous lymph-space which forms a sort of lymph- 

 jacket between the skin and the body-muscles (see Plate IV.). 

 Emerging from the region of the " armpit " can be seen a 

 large vein, the subclavian, dividing into a l?7'achial coming 

 down from the fore-limb, and a large musculo-cutaneous, 

 which arises by a mass of small veins covering ' the inner 

 surface of the skin. This vein brings aerated blood back 

 from the skin to the heart. 



Extending across from one mandible to the other is a 

 peculiar loose muscle, the mylohyoid. Further back the 

 sternum may be felt in the mid-ventral line, from the hind 

 end of which to the pelvis there runs a muscular band, the 

 rectus abdominalis. In the middle line of this muscle can 

 be seen a dark line caused by the underlying anterior 

 abdominal vein, 



A median incision can now be made from chin to pelvis 

 through the mylohyoid muscle, the sternum and the rectus 

 muscle (to one side of the anterior abdominal 

 vein). The body-cavitythus opened up has much 

 the same relationship as that of the skate (see Plate V.). ' 

 The abdominal cavity extends forw^ards to the level of the 

 oesophagus and backwards to the pelvis. The much 

 smaller pericardial cavity surrounds the heart and is com- 

 pletely separated from the abdominal cavity. As in the 

 skate, the organs are suspended in folds of peritoneum 

 which form dorsal mesenteries. 



The oesophagus enters the abdominal cavity anteriorly, 

 and soon swells into a stomach towards the left side. It is 

 covered by a large two-lobed liver with a 

 roundish gall-bladder. The stomach leads 

 into a duodenum into which there falls a bile-duct leading 

 down from the gall-bladder. Around the bile-duct is a 

 branched whitish gland, the pancreas, which opens by ducts 

 into it. The rest of the small intestine, called the ileum, is long, 

 of small calibre and coiled. It passes into a wide but short 



