is 



ANATOMY AND PHYSIOLOGY OK 



anterior belly of the expiratory muscle arises from the vertebral margins of the 



second and third intercostal spaces and from the second rib throughout its length. 



The posterior belly is like in origin to that of other Emydoidee; the muscular 



fibres are longer, however, and terminate squarely in the tendon, as docs also the 

 anterior belly. 



for convenience of reference, we have thrown into a tabular form the measure- 

 ments and muscular origins of the above genera. 



A glance at the table will show that in the most aquatic species of Emydoidse 

 the origin of the anterior belly of the muscle of expiration is from nearly the 

 middle of the shell; while in the less aquatic and terrestrial genera it is from the 

 forward part, and much more extensive. This arrangement is too uniform to be 

 passed by unnoticed, although our facts are so few that we cannot form any con- 

 clusions as to its generic meaning. Whether the same diversity of origin exists in 

 the genera of other families, and bears a similar relation to their family rank, and 

 also whether this origin is modified during the development of the turtle, we must, 

 leave for future inquiry. 



The neural apparatus of respiration in Chelonians, as in the Mammalia, consists 

 essentially of the nervus vagus supplying the larynx, of spinal nerves distributed 

 to the respiratory muscles of the trunk, and of the medulla oblongata, the common 

 centre through which the synchronous movements of the glottis and of the flanks 

 are incited and controlled. Between tin- ganglionic enlargements supplying the 

 upper and lower extremities, the spinal cord is attenuated, the nerves coming from 

 tlii- region being restricted, by the existence of ;t bony thorax, almost entirety to 

 those concerned in the movements of respiration. The disposition of the trunks 

 of these nerves closely resembles that of the intercostals in man. Escaping from the 

 spinal canal at the intervertebral foramina they traverse the carapace in parallel 

 lines between the rihs. giving off branches from time to time to their appropriate 

 muscles. By dissection and by mechanical irritation of the peripheral end of the 

 cut nerve, exciting contraction of different fibres, we have determined that the fila- 

 ments finally distributed to the expiratory muscle are derived from the first, second 

 and third dorsal nerves for the anterior belly, and from the fifth, sixth and seventhfor 

 the posterior belly. The sixth and seventh nerves are also the sources of supply to 

 the muscles of inspiration, the seventh being distributed over the inner or pelvic side, 



