The coraco-mandibularis, coraco-hyodeus, coraco-arcualis communis, and coraco-branchialis muscles should be dissected as a preliminary operation to following the ventral aorta and its branches. In front of the coraco-arcuales communes are three large longitudinal muscles. The median, unpaired one, arising from the fascia between the coraco-arcuales communes and inserted upon the posterior surface of the lower jaw, is the _coraco-mandibularis_. The other two, which lie dorsal to and outside of the coraco-mandibularis, are the _coraco-hyoidei_. They arise from the fasciae covering the anterior ends of the coraco-arcuales communes and posterior parts of the coraco-branchiales, and insert upon the basihyal. Dissect out the coraco-mandibularis and coraco-hyoidei, noting particularly the form and place of origin of the latter. Dorsal to the coraco-hyoidei are the first divisions of the right and left _coraco-branchialis_ muscles, which arise from fascia covering the anterior ends of the coraco-arcuales communes, and are inserted upon the ventral extremity of the ceratohyal cartilage. Notice that they pass dorsad to the anterior branches of the aorta, and that the aorta itself can be exposed between them. Remove the coraco-arcualis communis by dissecting it from the pectoral girdle and reflecting it forward. The other four divisions of the coraco-branchialis are now revealed, attached to the lateral surface of the pericardium and the lateral portion of the coracoid. The divisions of the muscle are clearly separated only near their insertions. The second, third, and fourth coraco-branchials are attached to the hypobranchial cartilages of the second, third and fourth visceral arches. The fifth division is inserted upon the lateral portion of the basibranchial and the expanded medial end of the fifth ceratobranchial. _The first_ aortic branch passes ventral to the first coraco-branchial. _The second_ aortic branch passes between the first and second coraco-branchials. _The third_ aortic branch passes between the second and third coraco-branchials. _The fourth_ aortic branch passes between the third and fourth coraco-branchials. Expose the dorsal ends of the gill arches by clearing away muscles and other tissues between the gill pouches and the spinal column. Two sets of four small muscles (interarcuales) will be found connected with the branchial cartilages. The second, third and fourth _medial interarcuales_ extend from the posterior surfaces of pharyngo-branchial cartilages 1, 2, and 3, to the dorsal surfaces of pharyngo-branchials 2, 3, 4, and 5. The first medial interarcuale arises from the under surface of the cranium and inserts on the upper end of the first pharyngo-branchial.