A smies of 15 rabbits had multiple intercostal clip electrodes implanted in the diaphragm and quadratus lumborum at open operation.Leads from the electrodes were passed to the back of the animals and soldered to a junction band. Simultaneous recordings of electromyographic activity and spirometry were made following recovery.The study revealed that the quadratus lumborum, acting simultaneously with the diaphragm, is an effective inspiratory muscle stabilizing the twelfth rib, converting i t into a fixed point from which the diaphragm acts. Very possibly the action of the quadratus pulls down the lower rib helping to increase the costo-diaphragmatic recess. Like the sternal, crural and costal portions of the diaphragm, the quadratus exerts a braking action to oypose the normal elastic recoil of the lungs during expiration.

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O m TEXT IlGUBE AND ONE PLATE ( W O FIQUBEB)

In his study of the development of behavior in mammals, Coghill ('38, '39) made observations upon pouch young opossums of early age. Previously ('18, '28), he had demonstrated the correlation of the development of structure with the development of function in amphibia. In the opossum he found most important the retarded development of the hindlimbs as compared with the advanced development of the forelimbs and head. Hartman ('20, '50) had observed the active use of the forelimb even before the time of birth and then at term in climbing into the marsupial pouch. Langworthy ('28) noted that in this maneuver the hindlimbs did not participate in the grasping movements. For one week after birth the young opossum does not move these limbs in response to stimulation nor spontaneously. Only passive movements are present during this period but upon or about the eighth day the hindlimbs become motile in response to stimuli. Studies upon the pathways and connections of the central nervous system in these early stages have been in progress (Hogg and Pankratz, '47). To investigate the relationships of the skeleton, the muscles and the peripheral nerves the present study was undertaken. METHODSSerial sections of several specimens of early ages were studied using the lower powers of the microscope to follow the nerves and skeletal elements and the muscles. To visualize these in three dimensions and at a magnification of 50 diameters, wax plate reconstructions were made after the method of Born (Bardeen, '01). Using two individuals, one of 4 days, in which the hindlimb was nonmotile, and one of 8 days which had shown passive movement but none in response to stimulation, models were made to show the skeletal and the nerve development of the hindlimb and the related spinal column. All pouch young studied had been tested by Coghill and Pankratz ('39) and the reactions recorded in their protocols and in motion pictures. They were then processed histologically and sectioned serially. In connection with microscopic study of the serial sections, the enlarged reconstructions allow description of this stage of development of the skeleton and of the nerve trunks. The muscles were studied in the sections but are not included in the reconstructions. A model to show them is a project for later execution.