JANE I. EOP.ERTSON. 
( 12 )^ where the posterior (dorsal) auriculo-ventricular pocket 
valve is homologous with the auriculo-ventricular plug 
of Lepi do siren (vide infra). 
Interventricular Septum. — Meanwhile the inter- 
ventricular septum and musculature are also appearing 
(Stage 30). Little subendothelial proliferations occur (Text- 
figs. 11 aud 16, a^. r.), connected with the tip of the auriculo- 
ventricular ridge, along the posterior (dorsal) and ventral 
walls of the ventricle somewhat to the left side. Almost 
immediately, however, other little muscular buds appear on 
the lateral walls as well (Text-fig. 16, m. b.). 
Text-fig. 16. 
Section through the ventricle at Stage 31 showing buds of 
ninscnlar tissue projecting into the ventricle, av. r. Anricnlo- 
ventricnlar ridge, m. h. Muscle buds. 
The last mentioned buds that are not from the first con- 
tinuous with the auriculo-ventricular ridge project into the 
lumen of the ventricle, and as their somewhat club-shaped 
tips converge, sooner or later neighbouring buds coalesce, 
forming irregular arches and meshes which all again 
converge on the central point d^appui formed by the tip 
of the auriculo-ventricular ridge as it appears in the auriculo- 
venti-icnlar aperture (d’ext-fig. 17). 
These converging arches thus form trabeculae that sweep 
on either side, from the posterior (dorsal) rim of the auriculo- 
ventricular aperture on to its lateral margins, and, mesially 
on to the anterior (ventral) margin of the bulbo-ventricular 
aperture. As the two apertures are situated antero-posteriorly. 
