ai4 



scraiNiD^. 



vessels. This ventral sac lies free round the intestines, and is fixed 

 by a peritoneal fold along the medial line of the abdomen. 



The way in which the peritoneum forms the base of the dorsal and 

 ventral system of air-vessels is the following, and will be illustrated 

 by the accompanying schematic sketch, giving a view of a cut, made 

 on the level of the posterior third 

 of the stomach. 



We may distinguish a parietal 

 and a visceral part of the perito- 

 neum, each being separated into 

 two lamlnce, an external and an 

 internaL 



1 . Peritoneum parietale. 



a. The external lamina (epp) 

 merely covers the inside of the ab- 

 dominal cavity and the kidneys, 

 which are situated outside the 

 peritoneal sac ; it is shining sil- 

 very, soft, and very easily torn ; 

 in the median line of the ventral 

 side it turns inside, forming a fold 

 of stronger structure, by which 

 the ventral sac of the system of 

 air-vessels is fixed, and which passes, 



b, into the internal lamina of the peritoneum parietale (ip p). This 

 part of the peritoneum has, Uke all the following, the stinicture and 

 firmness of a common serous membrane. It forms the outer part 

 of the ventral and dorsal sacs, being uninterrupted, and nowhere 

 pierced by aii'-vessels. 



2. Peritoneum viscerale. 



a. The lamina interna (ip v) covers all the abdominal intestines, 

 stomach (s), liver (I), &c., fixing them to one another by folds, as usual, 

 and surrounding the air-bla"dder on all sides. Now, enveloping each of 

 the appendages, and following them to their first bifurcation, it passes, 



b, into the lamina externa of the peritoneum viscerale (ep v) : 

 one part forms the inner side of the ventral sac, the other that of the 

 dorsal. Thus the visceral peritoneum is pierced by as many lioles as 

 there arc appendages of the air-bladder. Where the immediate con- 

 nexion between the visceral and the parietal peritoneum is, 1 could not 

 find ; but the principal point which I wish to show is, that both 

 the ventral and dorsal sacs are formed by a lamina of the visceral 

 and by another of the parietal peritoneum. The air-vessels are im- 

 bedded between these laminae — the dorsal vessels (d v) as well as the 

 ventral (v v) — in a stratum of cellular tissue, which on the dorsal side 

 is so thick, that it might be taken for a part of the air-bladder itself, 

 whilst in fact the small vessels only are in immediate contact with 

 the airrbladder. The ventral sac shows the same structure, but the 

 stratum of cellular tissue is thinner. Whilst the dorsal sac is situated 

 immediately on the back of the air-bladder, the ventral receives the 

 intestines in its cavity. 



Skeleton. — Owing to the bad condition of the skeleton, it is impos- 



