The carlicst contractions of thc erribryoiiic liearts which will he describecl in this commirnication, were observed in hangins drop cultures of whole rat cmbryos.The initiation of contraction has been observed in two other forms, namely, in tlic chick by Patteii aiid Kiramer ('33), Sabin ('20) and Johnstone ( ' 2 5 ) arid in Xmhlystoma by Copenhaver ( ' 3 7 ) . According to these authors, tlie first portion of the heart which hecomes active is the veiitricle, and the myocardium contracts yigorously for mine time before circulation of the blood is established. The development of functioii in the rat mill he seen to follow tlie same general plan. Certain differences, Irowcver, correlated with diffcrmeed in the morphological development will be described. A comparison of the structure of thc rat heart with that of other mammals at the same stage of development suggests that the type of functional activity observed in the rat may be characteristic of mammalian cmlxyos. Tii order to facilitate the study of tlic morphology of the heart and associated structures at the stage of hegiiining contractioii, a wax plate reconstruction was prcparecl of s r a t embryo of corresponding age fixed in the uterus.
X4TERIhIi AND IIETIIODSThe technique for removal of rat cnibr-j-os arid their preparation in hanging drop tissuc cultures has been described by Xcholas and Rrtdriick ( '34) aiid a few modifications 306
In this treatise Galen gives a synopsis of the description of the nerves contained in his long anatomical work "On Anatomical Procedures." He omits the olfactory nerves from the cranial group, considering them a part of the brain. Out of loyalty to his teacher, Marinos, he numbers seven cranial nerves but actually identifies ten, misconstruing the fourth, omitting the sixth, and describing all the others. The sympathetic is linked with the trigeminal but most parts of it are described. The spinal nerves and their plexuses are briefiy but quite accurately described. He leaves no doubt that he identified these nerves anatomically and understood much of their function.
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