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Show 492 MR. G. W. BUTLER ON THE [June 14, Thus, considering the relations of the lung to the body-cavity, we find that in the region anterior to the liver the cavity is reduced ; and, tracing our sections backwards, we find that the anterior part of the lung is surrounded on all sides by connective tissue. Then (still in the region of the heart) a small cavity appears on the outer side of the lung, which (Pp in fig. 1A), as we approach the apex of the heart and the anterior border of the liver, extends round dorsad of that organ. In sections that pass through the anterior apex of the liver, the lung is bounded ventrally by a sort of incipient fibrous-tissue " diaphragm," referable in part to a latero-anterior ligament of the liver, and in part to a proliferation of connective tissue that occurs on the ventral side of the lung, which we can trace extending backwards over the ventral surface of its at present free portion (* in fig. 2A). As remarked above, transverse sections taken anywhere else through the liver show the lung projecting freely into the common pleuroperitoneal cavity, which wraps round it dorsally and ventrally, in fact all round it, except on its left or mesial side where it is attached (fig. 2A). When, however, we follow the sections still farther back, behind the liver, we find that the posterior part of the lung burrows as it were into the connective tissue dorsad of the body-cavity, a little to the right of the aorta (fig. 3A). W e see, then, that at both ends there is a tendency to exclude the lung from the general body-cavity, and at the same time to obliterate the pleural cavity. Similarly, if, leaving the lung, we turn to the left side of this embryo and follow the sections backwards, we find that it is not till we reach about the middle of the liver that we see the oesophagus projecting into the peritoneal cavity. For the anterior part of its course it is for the most part surrounded by connective tissue (figs. 1A and 2A). Again; on the same left side of the body, just posterior to the left lobe of the liver, we find a foreshadowing of the " posthepatic septum," which later closes the liver-sacs posteriorly. This foreshadowing consists in a broadening and leftward extension over the stomach of the median ventral ligament. W e note also that behind the liver the body-cavity of either side is somewhat circumscribed (fig. 3A). § VI. (iii.). Embryo of Elaphis quadrilineatus, 15 cm. long. M y next stage is an Elaphis embryo 15 cm. long (Plate XXVIII. fig. B). I regret not having a stage intermediate between this and the preceding, or any embryo of another species of equivalent age. Still, I think that a careful comparison of the 11 cm. and 15 cm. stages leaves but little uncertainty as to how we ought to regard these peritoneal spaces of Snakes. Comparing the general features of the two embryos, we see that the head has now a less embryonic appearance, the lower jaw, for instance, being better developed. The umbilicus is further removed from the cloaca, and sections show us that the gall-bladder and |
