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PROFESSOR D. WATERSTON ON 
Langer, working on embryo fishes and reptiles and later on birds and mammals, 
identified a chamber in the heart possessing similar characters, and gave to it the 
name of bulbus cordis, a term which has been generally recognised and adopted. 
Thus Born at a later date substitutes the term bulbus cordis for the portion termed 
by His the conus arteriosus ; and Tandler, in describing the development of the 
human heart at an early stage, terms the descending limb of the Y-shaped loop the 
ventricular limb and the ascending the bulbus limb. 
The distinctive features of the bulbus cordis chamber in embryo hearts can be 
clearly laid down. 
(1) Its wall is composed of a muscular tissue similar to that of the myocardium 
of the ventricle. 
(2) It contains in its interior thickenings of subendocardial tissue, which form 
the “ bulbar cushions.” 
(3) In position it lies between the ventricle and the truncus arteriosus. 
GIreil has followed the changes which occur in the bulbus cordis in the developing 
heart of Lacerta, and in the crocodile ; and he has shown that in Lacerta it forms in 
its caudal portion a definite chamber in the ventricular part of the heart, from which 
arise the pulmonary artery and the left systemic aorta. 
It has also been recognised that in the mammalian heart, including man, the 
bulbus cordis forms at least a portion of the right ventricle (Keith, etc.) ; and Born 
derives from its upper part a portion at least of the pulmonary artery, as well as of 
1 the right ventricle. 
By some writers it is assumed that the bulbo-ventricular is synonymous with the 
interventricular furrow of the heart. 
Thus Mall ( Amer . Journ. of Anat., vol. xiii, p. 252), describing the heart of an 
embryo 3'5 mm. in length, states: “The lower connecting piece unites the left 
ventricle with the bulb, which later on gives rise to the right ventricle.” And again, 
in reference to the heart of an embryo 4^ mm. in length, he states : “ The trabecular 
system has extended into the bulbus — that is, into the right ventricle.” 
In examining a series of embryos such as the present one, one is very much 
struck by the definite characters shown throughout all the early stages of develop- 
ment by the “ bulbus cordis.” 
Its wall is composed of muscle tissue similar to that of the left ventricle, and 
this muscle tissue ceases abruptly at the line of junction of the bulbus with the 
truncus arteriosus. The interior shows at the earliest stages the loose subendocardial 
reticulum, which is later replaced by definite masses, the bulbar cushions, and it lies 
between the left ventricle and the truncus arteriosus. 
The principal features to be discussed are : (l) alteration in the direction of the 
bulbo-ventricular groove ; (2) the extent of the bulbar cushions ; and (3) the relation 
of the bulbar cushions to the right ventricle and to the definite muscular inter- 
ventricular septum. 
