222 



ELEMENTARY ANA TO MY. 



[LESS. 



We have seen that the branchial arches of Fishes form a 

 series of arcs beneath the head. Moreover they grow smaller 

 and more contracted from before backwards, i.e. post-axially. 



FIG 191. Skeleton of the Thorax of a Bird, showing the hypaxial processes, h, 

 descending, which are furnished with complete paraxial arches. 

 (For parts of sternum see Lesson II.) 



These arches are of the same essential nature as are the 

 hyoidean arch, the mandible, the palatine arch, and the trabe- 



FIG. 192. SKULL AND BRANCHIAL ARCHES OF A SHARK. 



b j b$, branchial arches ; k, hyoidean arch ; m, mandible;/?, palato-quadrate arch. 

 (From the College of Surgeons' Museum.) 



culae cranii, for (as we shall hereafter see) the relations of the 

 nerves and blood-vessels which skirt them are similar. 



In Fishes, the heart and great blood-vessels are outside 

 the branchial arches, and therefore (as these vessels indicate 

 the line of the pleuro-peritoneal division of the ventral laminae) 



