294 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the margin save the anterior. There is present also a depression on the 
surface of the ectoderm of the disc immediately beneath the bridge, and 
the cavity which lies between this surface and the under surface of the 
bridge is connected by a narrow canal with the cavity which surrounds 
the disc between the extra- germinal ectoderm and the endoderm. The 
bridge seems to grow not only by a proliferation of the ectoderm cells 
of the germinal disc, but also by additions from the adjacent cells of the 
extra-germinal area. The fate of the bridge seems to be that its free 
anterior margin finally meets the true ectoderm of the disc ; the structure 
then sinks down until it comes in contact with the underlying ectoderm, 
with which it finally fuses. 
The author discusses the possibility that the bridge may be homo- 
logous with a thickening of the “ Deckschicht ” or Rauber’s layer ; but 
it seems to him more probable, for reasons stated, that the bridge 
corresponds to the overgrowth along the dorsal side of Amphioxus. 
Whatever the interpretation of the bridge may be, we have the fact 
of its existence, and it is likely that it will be found to occur in other 
Mammals as well, such as the sheep. 
Development of Lymphatic Vessels.* — Prof. L. Ranvier has studied 
the development of the lymphatic vessels — hitherto almost quite unknown 
— in embryos of the pig, where they make their first appearance in 
embryos about 10 cm. in length. His conclusion is that the lymphatic 
system may be regarded as an immense vascular gland, having its origin 
in the venous system, and contributing to the veins its secretory product, 
which is the lymph. The lymphatic capillaries correspond to the 
secretory portion, the lymphatic trunks to the excretory canals of the 
gland. 
Development of Veins in the Head Region. | — Herr H. Salzer has 
studied this in the guinea-pig. The first distinct venous channel is 
median (vena cardinalis anterior ), and close to the neural canal. Then 
a lateral channel appears (vena capitis lateralis ), from the trigeminal to 
the hypoglossal, and the first-named vein, which anastomoses with it, 
disappears. When the skeletal rudiments have appeared, the blood from 
the anterior cerebral region leaves the cranial cavity by a vessel which 
is closely applied to the lateral side of the facial, while the blood from 
the posterior region follows a channel alongside of the vagus group. 
The two uiiite just at the posterior surface of the auditory labyrinth. 
The vessel running with the vagus is the rudiment of the subsequent 
root of the internal jugular, and soon becomes the only vein from the 
cranial cavity. But the author shows how veins from the orbit, &c., 
gradually become more prominent, and in a somewhat complicated 
maimer form the external jugular, which more or less completely 
replaces the internal jugular. The external jugular is thus subsequent 
to and independent of the internal jugular. Herr Salzer sketches the 
history of these veins throughout the Vertebrate series, and insists on 
the general similarity throughout. 
Operculum of Birds.J — Prof. N. Nassonow notes that the skin folds 
which he found in front of the hyoid arch in embryos of the African 
* Comptes Rendus, cxxi. (1895) pp. 1105-9. 
t Morphol. Jahrb., xxiii. (1895) pp. 232-55 (1 pi.). 
X Zool. Anzeig., xix. (1896) pp. 159-60. 
