340 CHORDATA. 
tympanic cavity. Further back still, on the ventral surface, 
is a small median longitudinal slit, called the g/o/t7s, leading 
into the lungs. Lastly, the wide wsophagus 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 brachial 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 zrated 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. Inthe 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-cavity thus opened up has much 
the same relationship as that of the skate (see Plate V.). 
The abdominal cavity extends forwards to the level of the 
cesophagus 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 cesophagus enters the abdominal cavity anteriorly, 
and soon swells into a stomach towards the left side. It is 
dinkeauary covered by a large two-lobed “ver with a 
‘ roundish gal/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 z/ewm, is long, 
of small calibre and coiled. It passes into a wide but short 
Colom. 
