146 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



2. The Placenta. Procure a placenta. Wear rubber gloves or 

 handle this organ only with instruments. Study its appearance and 

 draw a diagram to illustrate its position in the uterus. Divide the 

 umbilical cord and identify its constituent blood-vessels. Observe the 

 character of the outer and inner surfaces of the placenta. Note that the 

 umbilical vessels complete their subdivision before the substance of the 

 placenta is reached. Follow a cluster of vessels and separate the tissue 

 supplied by them from the tissue supplied by neighboring groups of 

 vessels. Suspend the fringed tissue so isolated in a beaker filled with 

 water. By this means one may reproduce the conditions normally 

 existing in this organ, the water representing the maternal blood with 

 which the fetal blood is in diffusion relation. 



3. The Respiratory Movements in Fishes. Carefully study the 

 opening and closing of the gill plates. What is the relation between 

 this movement and the movements of the floor of the mouth? Draw 

 diagrams to show the parts involved in these movements. Show the 

 position of the maxillary and bronchostegal valves during inspiration 

 and expiration. 



